fix hotreload时因为类型转换出错带来的白屏问题

lib/flutter_boost.dart

@@ -70,14 +70,20 @@ class FlutterBoost {
 
   static void onPageStart() {
     WidgetsBinding.instance.addPostFrameCallback((_) {
-      singleton.channel.invokeMethod<Map>('pageOnStart').then((Map pageInfo) {
-        if (pageInfo == null || pageInfo.isEmpty) return;
-
-        if (pageInfo.containsKey("name") &&
-            pageInfo.containsKey("params") &&
-            pageInfo.containsKey("uniqueId")) {
+      singleton.channel
+          .invokeMethod<Map<dynamic, dynamic>>('pageOnStart')
+          .then((Map<dynamic, dynamic> pageInfo) {
+        if (pageInfo == null || pageInfo.isEmpty) {
+          return;
+        }
+        if (pageInfo.containsKey('name') &&
+            pageInfo.containsKey('params') &&
+            pageInfo.containsKey('uniqueId')) {
           ContainerCoordinator.singleton.nativeContainerDidShow(
-              pageInfo["name"], pageInfo["params"], pageInfo["uniqueId"]);
+              pageInfo['name'] as String,
+              (pageInfo['params'] as Map<dynamic, dynamic>)
+                  .cast<String, dynamic>(),
+              pageInfo['uniqueId'] as String);
         }
       });
     });