Cancel the transitionend timer

+ To prevent ReactJS setState warnings involving unmounted components

Author: aaronlademann-wf

lib/src/component/abstract_transition.dart

@@ -314,6 +314,7 @@ abstract class AbstractTransitionComponent<T extends AbstractTransitionProps,
   void componentWillUnmount() {
     super.componentWillUnmount();
     _isUnmounted = true;
+    _cancelTransitionEndTimer();
     _cancelTransitionEventListener();
   }