Bug 1268453 - Use Android Gradle plugin 2.1. r=mcomella

MozReview-Commit-ID: 4Whi8k2kzz0

--HG--
extra : rebase_source : 95883b76c7088a9937b5b049ab0f0f4695306301
extra : histedit_source : 9918033b53c5716904e5b2db324445044d9090cf

build.gradle

@@ -33,7 +33,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.0.0'
+        classpath 'com.android.tools.build:gradle:2.1.0'
         classpath('com.stanfy.spoon:spoon-gradle-plugin:1.0.4') {
             // Without these, we get errors linting.
             exclude module: 'guava'