Upgrade to Android Gradle plugin 2.3.0

This mainly brings performance improvements in conjunction with newer
Gradle version.

Change-Id: I8bbcb7b3fa59b483d5f679732d7ee8f0e24168cd
diff --git a/build.gradle b/build.gradle
index d95bf48..40eb01d 100644
--- a/build.gradle
+++ b/build.gradle
@@ -12,7 +12,7 @@
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.2.0'
+        classpath 'com.android.tools.build:gradle:2.3.0'
         classpath 'com.github.ben-manes:gradle-versions-plugin:0.13.0'
 
         // NOTE: Do not place your application dependencies here; they belong