Fix JavaDocs of Single.doOnTerminate refer to onComplete notification (#6565)

Author: SupasinTatiyanupanwong

src/main/java/io/reactivex/Single.java

@@ -2501,13 +2501,13 @@ public final Single<T> doOnSubscribe(final Consumer<? super Disposable> onSubscr
      * <p>
      * <img width="640" height="305" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/doOnTerminate.png" alt="">
      * <p>
-     * This differs from {@code doAfterTerminate} in that this happens <em>before</em> the {@code onComplete} or
+     * This differs from {@code doAfterTerminate} in that this happens <em>before</em> the {@code onSuccess} or
      * {@code onError} notification.
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code doOnTerminate} does not operate by default on a particular {@link Scheduler}.</dd>
      * </dl>
-     * @param onTerminate the action to invoke when the consumer calls {@code onComplete} or {@code onError}
+     * @param onTerminate the action to invoke when the consumer calls {@code onSuccess} or {@code onError}
      * @return the new Single instance
      * @see <a href="http://reactivex.io/documentation/operators/do.html">ReactiveX operators documentation: Do</a>
      * @see #doOnTerminate(Action)