Update android version to 8

android/AndroidManifest.xml

 <?xml version="1.0"?>
-<manifest package="org.radar.app" xmlns:android="http://schemas.android.com/apk/res/android" android:versionName="0.7" android:versionCode="7" android:installLocation="auto">
+<manifest package="org.radar.app" xmlns:android="http://schemas.android.com/apk/res/android" android:versionName="0.8" android:versionCode="8" android:installLocation="auto">
     <!--<uses-sdk android:minSdkVersion="16" android:targetSdkVersion="28"/> -->
 
     <!-- The following comment will be replaced upon deployment with default permissions based on the dependencies of the application.