update gradle to 2.2

.travis.yml

@@ -15,7 +15,7 @@ cache:
     - $HOME/.gradle/caches/
     - $HOME/.gradle/wrapper/
     - $HOME/.m2
-    - $HOME/android-sdk-linux/
+    - $HOME/android-sdk-linux/licenses/
 
 before_cache:
   - rm -rf $HOME/.gradle/caches/modules-2/modules-2.lock

android/build.gradle

@@ -5,7 +5,7 @@ buildscript {
         jcenter()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.1.3'
+        classpath 'com.android.tools.build:gradle:2.2.0'
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files