Merge pull request #623 from HansMuller/dismissable-bug

Reset the Dimissable fade animation on slow flings

packages/flutter/lib/widgets/dismissable.dart

@@ -150,11 +150,14 @@ class Dismissable extends StatefulComponent {
     if (!_isActive)
       return EventDisposition.ignored;
 
-    if (_isHorizontalFlingGesture(event)) {
     _dragUnderway = false;
+    if (_isHorizontalFlingGesture(event)) {
       _dragX = event.velocityX.sign;
       _fadePerformance.fling(velocity: event.velocityX.abs() * _kFlingVelocityScale);
+    } else {
+      _fadePerformance.reverse();
     }
+
     return EventDisposition.processed;
   }