Bump Xamarin.Android.Tools

Also pointed back to the official repo, instead of my fork

.gitmodules

@@ -12,4 +12,4 @@
 	url = https://github.com/xamarin/Xamarin.MacDev.git
 [submodule "Xamarin.Android.Tools"]
 	path = external/Xamarin.Android.Tools
-	url = https://github.com/jonathanpeppers/xamarin-android-tools.git
+	url = https://github.com/xamarin/xamarin-android-tools.git

external/Xamarin.Android.Tools

@@ -1 +1 @@
-Subproject commit c8b7434bfe6221f0f1fb862fb339c8be616cee75
+Subproject commit 6a81bcb5130a2b68b51214f21c14b300d43711cb