docs(README): fix Travis CI link broken
docs(README): fix Travis CI link broken

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