Prevent installation on SD card, which currently fails

This is a stop-gap for #551. It would be nice if it worked, but for now stop
people getting into the broken state (and the app is small anyway).

app/src/main/AndroidManifest.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    android:installLocation="auto" tools:ignore="UnusedAttribute"
+    android:installLocation="internalOnly" tools:ignore="UnusedAttribute"
       xmlns:tools="http://schemas.android.com/tools">
     <supports-screens tools:ignore="UnusedAttribute"
           android:xlargeScreens="true"