docs(installation): change rxjs-es to just rxjs
docs(installation): change rxjs-es to just rxjs

That was old and needed to be updated months ago.
jayphelps/rxjs,jayphelps/rxjs,kwonoj/RxJS,ReactiveX/RxJS,trxcllnt/RxJS,ReactiveX/rxjs,jayphelps/rxjs,trxcllnt/RxJS,IgorMinar/RxJS,Brocco/RxJS,RxJS-CN/RxJS-Docs-CN,jayphelps/rxjs,ReactiveX/rxjs,martinsik/rxjs,martinsik/rxjs,ReactiveX/rxjs,Brocco/RxJS,ReactiveX/rxjs,ReactiveX/RxJS,SangKa/RxJS-Docs-CN,trxcllnt/RxJS,martinsik/rxjs,kwonoj/RxJS,benlesh/RxJS,benlesh/RxJS,trxcllnt/RxJS,RxJS-CN/RxJS-Docs-CN,SangKa/RxJS-Docs-CN,benlesh/RxJS,kwonoj/RxJS,ReactiveX/RxJS,SangKa/RxJS-Docs-CN,jayphelps/rxjs,RxJS-CN/RxJS-Docs-CN,benlesh/RxJS,kwonoj/RxJS,SangKa/RxJS-Docs-CN,Brocco/RxJS,IgorMinar/RxJS,ReactiveX/RxJS,RxJS-CN/RxJS-Docs-CN,Brocco/RxJS,martinsik/rxjs