update platform_channel package name (#9021)

* update platform_channel package name

* lowercase name

examples/platform_channel/android/app/src/androidTest/java/com/example/flutter/ExampleInstrumentedTest.java → examples/platform_channel/android/app/src/androidTest/java/com/example/platformchannel/ExampleInstrumentedTest.java

-package com.example.flutter;
+package com.example.platformchannel;
 
 import android.graphics.Bitmap;
 import android.support.test.InstrumentationRegistry;

examples/platform_channel/android/app/src/main/AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="com.example.flutter"
+    package="com.example.platformchannel"
     android:versionCode="1"
     android:versionName="0.0.1">
 

examples/platform_channel/android/app/src/main/java/com/example/flutter/MainActivity.java → examples/platform_channel/android/app/src/main/java/com/example/platformchannel/MainActivity.java

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-package com.example.flutter;
+package com.example.platformchannel;
 
 import android.content.ContextWrapper;
 import android.content.Intent;