fix MulticastProcessor javadoc comment (#6042)

Author: satoshun

src/main/java/io/reactivex/processors/MulticastProcessor.java

@@ -43,7 +43,7 @@
  *      the given prefetch amount and no reference counting behavior.</li>
  * <li>{@link #create(boolean)}: create an empty {@code MulticastProcessor} with
  *      {@link io.reactivex.Flowable#bufferSize() Flowable.bufferSize()} prefetch amount
- *      and no reference counting behavior.</li>
+ *      and an optional reference counting behavior.</li>
  * <li>{@link #create(int, boolean)}: create an empty {@code MulticastProcessor} with
  *      the given prefetch amount and an optional reference counting behavior.</li>
  * </ul>
@@ -174,7 +174,7 @@ public static <T> MulticastProcessor<T> create() {
 
     /**
      * Constructs a fresh instance with the default Flowable.bufferSize() prefetch
-     * amount and no refCount-behavior.
+     * amount and the optional refCount-behavior.
      * @param <T> the input and output value type
      * @param refCount if true and if all Subscribers have canceled, the upstream
      * is cancelled