chore(package.json): update coverage script to run on windows
chore(package.json): update coverage script to run on windows

relates to #465

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