message: chore(typings): improve catchError typings
diff: @@ -4,7 +4,7 @@ import { Observable } from '../Observable';
  import { OuterSubscriber } from '../OuterSubscriber';
  import { subscribeToResult } from '../util/subscribeToResult';
  -import { ObservableInput, OperatorFunction } from '../types';
  +import { ObservableInput, OperatorFunction, MonoTypeOperatorFunction } from '../types';
  /**
  * Catches errors on the observable to be handled by returning a new observable or throwing an error.
  @@ -63,6 +63,8 @@ import { ObservableInput, OperatorFunction } from '../types';
  * catch `selector` function.
  * @name catchError
  */
  +export function catchError<T>(selector: (err: any, caught: Observable<T>) => never): MonoTypeOperatorFunction<T>;
  +export function catchError<T, R>(selector: (err: any, caught: Observable<T>) => ObservableInput<R>): OperatorFunction<T, T | R>;
  export function catchError<T, R>(selector: (err: any, caught: Observable<T>) => ObservableInput<R>): OperatorFunction<T, T | R> {
  return function catchErrorOperatorFunction(source: Observable<T>): Observable<T | R> {
  const operator = new CatchOperator(selector);
  