etcdctl: fix watch -after-index parsing
etcdctl: fix watch -after-index parsing

It uses -after-index incorrectly now:

```
$ ./bin/etcdctl --debug watch -after-index 31 foo
Cluster-Endpoints: http://localhost:2379, http://localhost:4001
cURL Command: curl -X GET
http://localhost:2379/v2/keys/foo?recursive=false&wait=true&waitIndex=33
```

After this PR:

```
$ ./bin/etcdctl --debug watch -after-index 31 foo
Cluster-Endpoints: http://localhost:2379, http://localhost:4001
cURL Command: curl -X GET
http://localhost:2379/v2/keys/foo?recursive=false&wait=true&waitIndex=32
```

nkhare/etcd,sebrandon1/etcd,Eagle-X/etcd,ravigadde/etcd,CrazyJvm/etcd,akauppi/etcd,jonboulle/etcd,purpleidea/etcd,yudai/etcd,elimisteve/etcd,qqsun8819/etcd,improbable-io/etcd,lzbgt/etcd,chenbaihu/etcd,zaphod-concur/etcd,glycerine/etcd,sebrandon1/etcd,vimalk78/etcd,hroyrh/etcd,fanminshi/etcd,betawaffle/etcd,SivagnanamCiena/etcd,rnaveiras/etcd,akauppi/etcd,axingblog/etcd,jchauncey/etcd,msanterre/etcd,tamird/etcd,imzhulei/etcd,mickep76/etcd,njucslqq/etcd,lorneli/etcd,freeloop1114/etcd,asim/etcd,fasaxc/etcd,gyuho/etcd,ajityagaty/etcd,a-robinson/etcd,iamqizhao/etcd,ajityagaty/etcd,rchicoli/etcd,whuwxl/etcd,coreos/etcd,glevand/coreos--etcd,polvi/etcd,zaphod-concur/etcd,wantonsolutions/dinv-etcd,shawnps/etcd,delkyd/etcd,Yhgenomics/etcd,jlamillan/etcd,giantswarm/etcd,mitake/etcd,kkaneda/etcd,HideoYamauchi/etcd,shakefu/etcd,arthurcolle/etcd,asim/etcd,lzbgt/etcd,xiang90/etcd,raoofm/etcd,etcd-io/etcd,dalanlan/etcd,lorneli/etcd,plasticbox/etcd,mike-lerch/etcd,wantonsolutions/dinv-etcd,dnaeon/etcd,etcd-io/etcd,achanda/etcd,cchamplin/etcd,mitake/etcd,svdata/etcd,linuxcer/etcd,arthurcolle/etcd,hongchaodeng/etcd,jlamillan/etcd,nkhare/etcd,ktateish/etcd,youxidev/etcd,TheHippo/etcd,snailwalker/etcd,improbable-io/etcd,oscarrr110/etcd,mkumatag/etcd,chipironcin/etcd,cockroachdb/etcd,jefby/etcd,bluebreezecf/etcd,honeyqa/etcd,onlyjob/etcd,bdarnell/etcd,Eagle-X/etcd,armstrongli/etcd,joshix/etcd,vimalk78/etcd,westhood/etcd,yyljlyy/etcd,openedbox/etcd,beni55/etcd,endocode/etcd,xychu/etcd,mqliang/etcd,buaazp/etcd,Winslett/etcd,SivagnanamCiena/etcd,spacejam/etcd,combk8s/etcd,buaazp/etcd,junxu/etcd,glycerine/etcd,hongbinz/etcd,insequent/etcd,luxas/etcd,whuwxl/etcd,sebschrader/etcd,OyTao/etcd_learning,jeremyeder/etcd,etcd-io/etcd,visheshnp/etcd,StorReduce/etcd,visheshnp/etcd,fasaxc/etcd,linuxcer/etcd,gityf/etcd,Timer/etcd,insionng/etcd,mkumatag/etcd,cognusion/etcd,cognusion/etcd,sofuture/etcd,yyljlyy/etcd,insionng/etcd,delkyd/etcd,axingblog/etcd,iamqizhao/etcd,rnaveiras/etcd,endocode/etcd,swingbach/etcd,spacejam/etcd,bdarnell/etcd,glevand/coreos--etcd,insequent/etcd,gyuho/etcd,Winslett/etcd,dnaeon/etcd,raoofm/etcd,li-ang/etcd,giantswarm/etcd,mqliang/etcd,siddontang/etcd,gouyang/etcd,youxidev/etcd,yudai/etcd,lumjjb/etcd,imzhulei/etcd,ajityagaty/etcd,TheHippo/etcd,kingland/etcd,sofuture/etcd,sayden/etcd,wowsoso/etcd,sayden/etcd,mkumatag/etcd,mike-lerch/etcd,msanterre/etcd,gouyang/etcd,heyitsanthony/etcd,rchicoli/etcd,fgbreel/etcd,tguangch/etcd,fasaxc/etcd,fgbreel/etcd,qqsun8819/etcd,xychu/etcd,polvi/etcd,combk8s/etcd,YuleiXiao/etcd,plasticbox/etcd,wfxiang08/etcd,ktateish/etcd,rnaveiras/etcd,svdata/etcd,jeremyeder/etcd,honeyqa/etcd,xdlinear/etcd,cchamplin/etcd,tangkun75/etcd,lumjjb/etcd,sinsharat/etcd,jchauncey/etcd,achanda/etcd,joshix/etcd,sebschrader/etcd,xiang90/etcd,es-chow/etcd,gae123/etcd,nekto0n/etcd,openedbox/etcd,steveeJ/etcd,wfxiang08/etcd,chipironcin/etcd,purpleidea/etcd,wantonsolutions/dinv-etcd,tempbottle/etcd,hongbinz/etcd,kingland/etcd,jefby/etcd,heyitsanthony/etcd,es-chow/etcd,gityf/etcd,luxas/etcd,handsomesun/etcd,njharman/etcd,gae123/etcd,beni55/etcd,swingbach/etcd,YuleiXiao/etcd,steveeJ/etcd,li-ang/etcd,sinsharat/etcd,fanminshi/etcd,wowsoso/etcd,elimisteve/etcd,tangkun75/etcd,kkaneda/etcd,chenbaihu/etcd,dannysauer/etcd,yichengq/etcd,nekto0n/etcd,tguangch/etcd,OyTao/etcd_learning,jonboulle/etcd,pauldallen/etcd,tamird/etcd,onlyjob/etcd,xdlinear/etcd,junxu/etcd,a-robinson/etcd,dalanlan/etcd,shawnps/etcd,hongchaodeng/etcd,mqliang/etcd,Yhgenomics/etcd,bluebreezecf/etcd,snailwalker/etcd,tempbottle/etcd,njharman/etcd,CrazyJvm/etcd,HideoYamauchi/etcd,njucslqq/etcd,pauldallen/etcd,dannysauer/etcd,betawaffle/etcd,siddontang/etcd,mickep76/etcd,Timer/etcd,coreos/etcd,ravigadde/etcd,westhood/etcd,oscarrr110/etcd,hroyrh/etcd,handsomesun/etcd,yichengq/etcd,cockroachdb/etcd,shakefu/etcd,armstrongli/etcd,freeloop1114/etcd,StorReduce/etcd