fix(Symbol.observable): make observable declaration readonly (#3697) (#3773)
fix(Symbol.observable): make observable declaration readonly (#3697) (#3773)


benlesh/RxJS,kwonoj/RxJS,martinsik/rxjs,kwonoj/RxJS,martinsik/rxjs,trxcllnt/RxJS,ReactiveX/rxjs,trxcllnt/RxJS,ReactiveX/RxJS,ReactiveX/RxJS,martinsik/rxjs,ReactiveX/RxJS,kwonoj/RxJS,Brocco/RxJS,trxcllnt/RxJS,kwonoj/RxJS,ReactiveX/rxjs,martinsik/rxjs,benlesh/RxJS,Brocco/RxJS,ReactiveX/RxJS,Brocco/RxJS,benlesh/RxJS,benlesh/RxJS,trxcllnt/RxJS,ReactiveX/rxjs,Brocco/RxJS,ReactiveX/rxjs