add to c_str on std::string parameter

Author: dacianf

shell/platform/darwin/ios/framework/Source/FlutterPlatformViews.mm

@@ -143,7 +143,7 @@
         errorWithCode:@"unregistered_view_type"
               message:[NSString stringWithFormat:@"A UIKitView widget is trying to create a "
                                                  @"PlatformView with an unregistered type: < %s >",
-                                                 viewType]
+                                                 viewType.c_str()]
               details:@"If you are the author of the PlatformView, make sure `registerViewFactory`"
                       @"is invoked.\n"
                       @"See: "