use latest 2.2.1 gradle/Android plugin

build.gradle

@@ -10,7 +10,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.2.0'
+        classpath 'com.android.tools.build:gradle:2.2.1'
     }
 }