Fix format Errors

* fix format errors in OneSignalPlugin.java, OneSignalPlugin.m and mock_channel.dart

Author: tanaynigam

android/src/main/java/com/onesignal/flutter/OneSignalPlugin.java

@@ -341,7 +341,7 @@ public void onFailure(OneSignal.OSSMSUpdateError error) {
 
   private void setLanguage(MethodCall call, final Result result) {
     String language = call.argument("language");
-    if(language != null && language.length() == 0)
+    if (language != null && language.length() == 0)
       language = null;
 
       OneSignal.setLanguage(language);

ios/Classes/OneSignalPlugin.m

@@ -324,8 +324,9 @@ - (void)removeExternalUserId:(FlutterMethodCall *)call withResult:(FlutterResult
 
 - (void)setLanguage:(FlutterMethodCall *)call withResult:(FlutterResult)result {
     id language = call.arguments[@"language"];
-    if (language == [NSNull null])
+    if (language == [NSNull null]) {
         language = nil;
+    }
 
     [OneSignal setLanguage:language];
 }

test/mock_channel.dart

@@ -68,7 +68,7 @@ class OneSignalMockChannelController {
         this.state.externalId = null;
         return {"success" : true};
       case "OneSignal#setLanguage":
-        this.state.language = (call.arguments as Map<dynamic, dynamic>)['language'] as String?;;
+        this.state.language = (call.arguments as Map<dynamic, dynamic>)['language'] as String?;
         return {"success" : true};
     }
   }