Added Google Maps sample code (#1671)

* Added Google Maps sample code

* Updated per @domesticmouse review

* Updated dependabot and pubspec for Dart 2.19

google_maps/test/widget_test.dart

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2019 Google LLC
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:google_maps_in_flutter/main.dart';
+
+void main() {
+  testWidgets('Do nothing test', (tester) async {
+    // Build our app and trigger a frame.
+    await tester.pumpWidget(const MyApp());
+  });
+}