Use 2.2.0-alpha1

Change-Id: I3e8bfb23b15e49b13d543f49ff897a1f8bee20b1
diff --git a/build.gradle b/build.gradle
index 9832ab9..a58ad47 100644
--- a/build.gradle
+++ b/build.gradle
@@ -9,7 +9,7 @@
         maven { url "../../prebuilts/maven_repo/android" }
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.1.0'
+        classpath 'com.android.tools.build:gradle:2.2.0-alpha1'
     }
 }