Bump versionCode of SkyDemo.apk to avoid downgrade warning.

sky/apk/demo/AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2015 The Chromium Authors. All rights reserved.
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file.
  -->
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="org.domokit.sky.demo"
-    android:versionCode="3"
+    android:versionCode="7"
     android:versionName="0.0.1">
 
     <uses-sdk android:minSdkVersion="14" android:targetSdkVersion="21" />
     <uses-permission android:name="android.permission.INTERNET"/>
     <uses-feature android:name="android.hardware.sensor.accelerometer" android:required="true" />
 
     <application android:icon="@mipmap/ic_launcher" android:name="SkyDemoApplication" android:label="Sky">
         <activity android:name="SkyDemoActivity"
                   android:launchMode="singleTask"
                   android:theme="@android:style/Theme.Holo.Light.NoActionBar"
                   android:configChanges="orientation|keyboardHidden|keyboard|screenSize"
                   android:hardwareAccelerated="true">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN"/>
                 <category android:name="android.intent.category.LAUNCHER"/>
             </intent-filter>
             <intent-filter>
                 <action android:name="android.intent.action.VIEW"/>
                 <category android:name="android.intent.category.DEFAULT" />
                 <data android:scheme="sky" />
             </intent-filter>
         </activity>
     </application>
  </manifest>