AndroidManifest.xml: disable auto-backup of (encrypted) app data

Android 6.0 and later automatically backs up app data and allow the user
to restore it when setting up a new device. Unfortunately, the app data
is encrypted with a device specific master key, rendering the data
unreadable on the second device.

Apply the allowBackup=false hammer since we only store device-specific
(logs) and sensitive (private keys, authentication tokens) data for now.

Fixes tailscale/tailscale#732

Signed-off-by: Elias Naur <mail@eliasnaur.com>

android/src/main/AndroidManifest.xml

@@ -8,7 +8,7 @@
 	<uses-feature android:name="android.hardware.type.pc" android:required="false"/>
 
 	<application android:label="Tailscale" android:icon="@mipmap/ic_launcher" android:roundIcon="@mipmap/ic_launcher_round"
-		android:name=".App">
+		android:name=".App" android:allowBackup="false">
 		<activity android:name="org.gioui.GioActivity"
 			android:label="@string/app_name"
 			android:theme="@style/Theme.GioApp"