java/com/tailscale/ipn: make App Android 5.1 compatible

Fragment.commitNow doesn't exist on Android 5.1. Calling commit and then all
flushing pending transactions is just as good, because we're not using any
other fragments.

Updates tailscale/tailscale#577

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

android/src/main/java/com/tailscale/ipn/App.java

@@ -136,7 +136,8 @@ public class App extends Application {
 		Activity act = (Activity)view.getContext();
 		FragmentTransaction ft = act.getFragmentManager().beginTransaction();
 		ft.add(new Peer(), "Peer");
-		ft.commitNow();
+		ft.commit();
+		act.getFragmentManager().executePendingTransactions();
 	}
 
 	boolean isChromeOS() {