2.x: Fixed Javadoc for Disposables.fromFuture (#4744)

* Fixed Javadoc for Disposables.fromFuture

* Missed a runnable

Author: falcon71

src/main/java/io/reactivex/disposables/Disposables.java

@@ -66,9 +66,9 @@ public static Disposable fromFuture(Future<?> future) {
     }
 
     /**
-     * Construct a Disposable by wrapping a Runnable that is
-     * executed exactly once when the Disposable is disposed.
-     * @param future the Runnable to wrap
+     * Construct a Disposable by wrapping a Future that is
+     * cancelled exactly once when the Disposable is disposed.
+     * @param future the Future to wrap
      * @param allowInterrupt if true, the future cancel happens via Future.cancel(true)
      * @return the new Disposable instance
      */