chore(build): copy source for sourcemaps
chore(build): copy source for sourcemaps

closes #1089

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