Resolved Dart Analysis errors (#138)

* Resolved Dat Analysis errors

* Resolved Dart Analysis errors

lib/src/chewie_player.dart

@@ -239,8 +239,7 @@ class ChewieController extends ChangeNotifier {
   final List<DeviceOrientation> deviceOrientationsAfterFullScreen;
 
   static ChewieController of(BuildContext context) {
-    final _ChewieControllerProvider chewieControllerProvider =
-        context.inheritFromWidgetOfExactType(_ChewieControllerProvider);
+    final chewieControllerProvider = _ChewieControllerProvider.of(context);
 
     return chewieControllerProvider.controller;
   }
@@ -325,6 +324,9 @@ class _ChewieControllerProvider extends InheritedWidget {
 
   final ChewieController controller;
 
+  static _ChewieControllerProvider of(BuildContext context) => context.inheritFromWidgetOfExactType(_ChewieControllerProvider) as _ChewieControllerProvider;
+
+
   @override
   bool updateShouldNotify(_ChewieControllerProvider old) =>
       controller != old.controller;

lib/src/cupertino_progress_bar.dart

@@ -51,7 +51,7 @@ class _VideoProgressBarState extends State<CupertinoVideoProgressBar> {
   @override
   Widget build(BuildContext context) {
     void seekToRelativePosition(Offset globalPosition) {
-      final RenderBox box = context.findRenderObject();
+      final box = context.findRenderObject() as RenderBox;
       final Offset tapPos = box.globalToLocal(globalPosition);
       final double relative = tapPos.dx / box.size.width;
       final Duration position = controller.value.duration * relative;

lib/src/material_progress_bar.dart

@@ -51,7 +51,7 @@ class _VideoProgressBarState extends State<MaterialVideoProgressBar> {
   @override
   Widget build(BuildContext context) {
     void seekToRelativePosition(Offset globalPosition) {
-      final RenderBox box = context.findRenderObject();
+      final box = context.findRenderObject() as RenderBox;
       final Offset tapPos = box.globalToLocal(globalPosition);
       final double relative = tapPos.dx / box.size.width;
       final Duration position = controller.value.duration * relative;