CLI: Adding shebang to setup_env.sh script
CLI: Adding shebang to setup_env.sh script

Summary:
Adding shebang to local-cli's setup_env script.

Depending how your *nix environment is setup, running `react-native bundle` will throw this error:

```
Error: spawnSync /opt/build/in/node_modules/react-native/local-cli/setup_env.sh Unknown system error -8
    at exports._errnoException (util.js:1022:11)
    at spawnSync (child_process.js:461:20)
    at Object.execFileSync (child_process.js:498:13)
    at repl:1:14
    at sigintHandlersWrap (vm.js:22:35)
    at sigintHandlersWrap (vm.js:96:12)
    at ContextifyScript.Script.runInThisContext (vm.js:21:12)
    at REPLServer.defaultEval (repl.js:346:29)
    at bound (domain.js:280:14)
    at REPLServer.runBound [as eval] (domain.js:293:12)
```

In my case I was running react-native on docker (using alpine-node:6 as base image).
Closes https://github.com/facebook/react-native/pull/12173

Differential Revision: D5154069

Pulled By: shergin

fbshipit-source-id: acf2a21499b4a57310afd06b57386e7900662b7d

facebook/react-native,myntra/react-native,kesha-antonov/react-native,exponentjs/react-native,peterp/react-native,negativetwelve/react-native,rickbeerendonk/react-native,exponentjs/react-native,tszajna0/react-native,cpunion/react-native,gilesvangruisen/react-native,myntra/react-native,myntra/react-native,makadaw/react-native,shrutic123/react-native,javache/react-native,facebook/react-native,farazs/react-native,exponent/react-native,facebook/react-native,ptmt/react-native-macos,pandiaraj44/react-native,facebook/react-native,exponent/react-native,forcedotcom/react-native,arthuralee/react-native,exponentjs/react-native,negativetwelve/react-native,shrutic123/react-native,forcedotcom/react-native,PlexChat/react-native,brentvatne/react-native,gilesvangruisen/react-native,cdlewis/react-native,hoastoolshop/react-native,hammerandchisel/react-native,kesha-antonov/react-native,brentvatne/react-native,peterp/react-native,Bhullnatik/react-native,Ehesp/react-native,Bhullnatik/react-native,cpunion/react-native,PlexChat/react-native,negativetwelve/react-native,brentvatne/react-native,skevy/react-native,negativetwelve/react-native,frantic/react-native,tszajna0/react-native,rickbeerendonk/react-native,frantic/react-native,Bhullnatik/react-native,doochik/react-native,exponentjs/react-native,janicduplessis/react-native,javache/react-native,kesha-antonov/react-native,tszajna0/react-native,facebook/react-native,forcedotcom/react-native,gilesvangruisen/react-native,pandiaraj44/react-native,hammerandchisel/react-native,facebook/react-native,thotegowda/react-native,negativetwelve/react-native,exponentjs/react-native,makadaw/react-native,kesha-antonov/react-native,myntra/react-native,mironiasty/react-native,jevakallio/react-native,arthuralee/react-native,exponent/react-native,mironiasty/react-native,Ehesp/react-native,mironiasty/react-native,hoangpham95/react-native,Ehesp/react-native,jevakallio/react-native,javache/react-native,mironiasty/react-native,rickbeerendonk/react-native,cdlewis/react-native,tszajna0/react-native,negativetwelve/react-native,exponentjs/react-native,jevakallio/react-native,rickbeerendonk/react-native,janicduplessis/react-native,Guardiannw/react-native,thotegowda/react-native,forcedotcom/react-native,cdlewis/react-native,hammerandchisel/react-native,gilesvangruisen/react-native,Ehesp/react-native,exponentjs/react-native,dikaiosune/react-native,kesha-antonov/react-native,Livyli/react-native,PlexChat/react-native,Livyli/react-native,kesha-antonov/react-native,thotegowda/react-native,hoangpham95/react-native,Ehesp/react-native,javache/react-native,exponent/react-native,forcedotcom/react-native,doochik/react-native,skevy/react-native,javache/react-native,hammerandchisel/react-native,hoastoolshop/react-native,brentvatne/react-native,rickbeerendonk/react-native,Livyli/react-native,tszajna0/react-native,myntra/react-native,PlexChat/react-native,frantic/react-native,thotegowda/react-native,arthuralee/react-native,makadaw/react-native,shrutic123/react-native,Ehesp/react-native,farazs/react-native,janicduplessis/react-native,cdlewis/react-native,farazs/react-native,ptmt/react-native-macos,javache/react-native,tszajna0/react-native,formatlos/react-native,myntra/react-native,ptmt/react-native-macos,kesha-antonov/react-native,Livyli/react-native,hammerandchisel/react-native,hoangpham95/react-native,thotegowda/react-native,makadaw/react-native,Bhullnatik/react-native,cdlewis/react-native,facebook/react-native,ptmt/react-native-macos,negativetwelve/react-native,myntra/react-native,dikaiosune/react-native,skevy/react-native,brentvatne/react-native,hammerandchisel/react-native,formatlos/react-native,exponent/react-native,peterp/react-native,cdlewis/react-native,negativetwelve/react-native,skevy/react-native,pandiaraj44/react-native,mironiasty/react-native,forcedotcom/react-native,formatlos/react-native,janicduplessis/react-native,shrutic123/react-native,hoangpham95/react-native,myntra/react-native,peterp/react-native,arthuralee/react-native,thotegowda/react-native,doochik/react-native,doochik/react-native,Livyli/react-native,cdlewis/react-native,frantic/react-native,mironiasty/react-native,Livyli/react-native,rickbeerendonk/react-native,exponentjs/react-native,farazs/react-native,ptmt/react-native-macos,janicduplessis/react-native,Bhullnatik/react-native,Livyli/react-native,rickbeerendonk/react-native,frantic/react-native,formatlos/react-native,farazs/react-native,kesha-antonov/react-native,PlexChat/react-native,rickbeerendonk/react-native,facebook/react-native,hoastoolshop/react-native,peterp/react-native,cdlewis/react-native,makadaw/react-native,ptmt/react-native-macos,formatlos/react-native,jevakallio/react-native,hoangpham95/react-native,makadaw/react-native,farazs/react-native,pandiaraj44/react-native,peterp/react-native,PlexChat/react-native,jevakallio/react-native,Guardiannw/react-native,javache/react-native,forcedotcom/react-native,cpunion/react-native,jevakallio/react-native,gilesvangruisen/react-native,javache/react-native,doochik/react-native,formatlos/react-native,cpunion/react-native,tszajna0/react-native,brentvatne/react-native,skevy/react-native,mironiasty/react-native,skevy/react-native,Bhullnatik/react-native,janicduplessis/react-native,makadaw/react-native,jevakallio/react-native,cdlewis/react-native,javache/react-native,brentvatne/react-native,makadaw/react-native,Guardiannw/react-native,PlexChat/react-native,gilesvangruisen/react-native,facebook/react-native,skevy/react-native,formatlos/react-native,brentvatne/react-native,Guardiannw/react-native,mironiasty/react-native,exponent/react-native,hammerandchisel/react-native,hoastoolshop/react-native,PlexChat/react-native,skevy/react-native,doochik/react-native,myntra/react-native,Bhullnatik/react-native,formatlos/react-native,tszajna0/react-native,negativetwelve/react-native,hoastoolshop/react-native,shrutic123/react-native,pandiaraj44/react-native,pandiaraj44/react-native,Guardiannw/react-native,Livyli/react-native,pandiaraj44/react-native,peterp/react-native,farazs/react-native,rickbeerendonk/react-native,dikaiosune/react-native,dikaiosune/react-native,hammerandchisel/react-native,cpunion/react-native,dikaiosune/react-native,gilesvangruisen/react-native,shrutic123/react-native,Bhullnatik/react-native,peterp/react-native,pandiaraj44/react-native,janicduplessis/react-native,janicduplessis/react-native,forcedotcom/react-native,dikaiosune/react-native,jevakallio/react-native,formatlos/react-native,dikaiosune/react-native,thotegowda/react-native,hoangpham95/react-native,cpunion/react-native,makadaw/react-native,hoastoolshop/react-native,shrutic123/react-native,hoastoolshop/react-native,exponent/react-native,gilesvangruisen/react-native,farazs/react-native,hoangpham95/react-native,hoastoolshop/react-native,doochik/react-native,kesha-antonov/react-native,jevakallio/react-native,mironiasty/react-native,cpunion/react-native,arthuralee/react-native,Guardiannw/react-native,ptmt/react-native-macos,Ehesp/react-native,farazs/react-native,doochik/react-native,cpunion/react-native,hoangpham95/react-native,doochik/react-native,Guardiannw/react-native,dikaiosune/react-native,shrutic123/react-native,ptmt/react-native-macos,Ehesp/react-native,exponent/react-native,thotegowda/react-native,Guardiannw/react-native,brentvatne/react-native