Don't call process.exit(0) on success. (#11)
Don't call process.exit(0) on success. (#11)

This causes commands like `optimize-js large-file.js` to not output the full output to stdout.

To repro:
```
$ curl -O https://code.jquery.com/jquery-3.0.0.min.js
$ optimize-js jquery-3.0.0.min.js  | wc
// 3     982   65536
$ optimize-js jquery-3.0.0.min.js > foo.js
$ cat foo.js | wc
//  5    1312   86638
```
nolanlawson/optimize-js,nolanlawson/optimize-js,nolanlawson/optimize-js