chore(package.json): add watch task for source changes
chore(package.json): add watch task for source changes

- watch task monitors source change to trigger build automatically
- lint executed prior to build test

closes #494, #495

RxJS-CN/RxJS-Docs-CN,Brocco/RxJS,justinwoo/RxJS,elliotschi/rxjs,justinwoo/RxJS,kwonoj/RxJS,martinsik/rxjs,RxJS-CN/RxJS-Docs-CN,ReactiveX/RxJS,adrianomelo/RxJSNext,jadbox/RxJS,jayphelps/rxjs,RxJS-CN/RxJS-Docs-CN,jayphelps/rxjs,justinwoo/RxJS,kwonoj/RxJS,justinwoo/RxJS,IgorMinar/RxJS,mattpodwysocki/RxJS,jadbox/RxJS,jadbox/RxJS,adrianomelo/RxJS-1,trxcllnt/RxJS,kwonoj/RxJS,staltz/RxJSNext,robwormald/RxJS,mattpodwysocki/RxJS,staltz/RxJSNext,elliotschi/rxjs,figueredo/RxJS,gluck/RxJS,adrianomelo/RxJSNext,saneyuki/RxJS,jinroh/RxJS,benlesh/RxJS,gluck/RxJS,adrianomelo/RxJSNext,figueredo/RxJS,adrianomelo/RxJSNext,trxcllnt/RxJS,figueredo/RxJS,adrianomelo/RxJS-1,ReactiveX/rxjs,martinsik/rxjs,SangKa/RxJS-Docs-CN,jadbox/RxJS,kwonoj/RxJS,Brocco/RxJS,ReactiveX/RxJS,benlesh/RxJS,Brocco/RxJS,Igorbek/rxjs5,jinroh/RxJS,adrianomelo/RxJS-1,elliotschi/rxjs,ReactiveX/rxjs,saneyuki/RxJS,Igorbek/rxjs5,ReactiveX/rxjs,benlesh/RxJS,jinroh/RxJS,benlesh/RxJS,jayphelps/rxjs,Igorbek/rxjs5,mattpodwysocki/RxJS,SangKa/RxJS-Docs-CN,RxJS-CN/RxJS-Docs-CN,gluck/RxJS,staltz/RxJSNext,robwormald/RxJS,gluck/RxJS,staltz/RxJSNext,SangKa/RxJS-Docs-CN,ReactiveX/rxjs,figueredo/RxJS,Igorbek/rxjs5,trxcllnt/RxJS,jayphelps/rxjs,robwormald/RxJS,martinsik/rxjs,SangKa/RxJS-Docs-CN,adrianomelo/RxJS-1,Brocco/RxJS,martinsik/rxjs,ReactiveX/RxJS,ReactiveX/RxJS,mattpodwysocki/RxJS,robwormald/RxJS,jinroh/RxJS,elliotschi/rxjs,jayphelps/rxjs,trxcllnt/RxJS,IgorMinar/RxJS