Merge pull request #32 from SpencerLindemuth/master

Add cleaner context check

Author: rayliverified

lib/responsive_wrapper.dart

@@ -461,7 +461,7 @@ class _ResponsiveWrapperState extends State<ResponsiveWrapper>
     // The required MediaQueryData is only available
     // on the next frame for physical dimension changes.
     WidgetsBinding.instance.addPostFrameCallback((_) {
-      if (context != null) {
+      if (mounted) {
         setDimensions();
         setState(() {});
       }