fix(operator/do): fix typings

Author: Brooooooklyn

src/operator/do.ts

@@ -48,7 +48,7 @@ import { TeardownLogic } from '../Subscription';
  * @owner Observable
  */
 /* tslint:disable:max-line-length */
-export function _do<T>(next: (x: T) => void, error?: (e: any) => void, complete?: (this: Observable<T>) => void): Observable<T>;
+export function _do<T>(this: Observable<T>, next: (x: T) => void, error?: (e: any) => void, complete?: () => void): Observable<T>;
 export function _do<T>(this: Observable<T>, observer: PartialObserver<T>): Observable<T>;
 /* tslint:disable:max-line-length */
 export function _do<T>(this: Observable<T>, nextOrObserver?: PartialObserver<T> | ((x: T) => void),