fix #642

lib/src/foundation/share_models.dart

@@ -338,7 +338,7 @@ class WeChatImageToShare with _Argument {
   /// [uint8List] is available on both  iOS and Android
   /// [localImagePath] only available on  Android, if [uint8List] is null, [localImagePath] must not be null;
   /// if [uint8List] and [localImagePath] are both provided on android, [uint8List] will be used.
-  WeChatImageToShare(this.uint8List, this.localImagePath, this.imgDataHash) {
+  WeChatImageToShare({this.uint8List, this.localImagePath, this.imgDataHash}) {
     if (Platform.isIOS) {
       assert(uint8List != null);
     }