TravisCI: cache support

Author: duangsuse

.travis.yml

@@ -7,3 +7,12 @@ android:
     - extra-android-m2repository
 
 script: ./gradlew check
+before_cache:
+  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
+  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
+cache:
+  directories:
+    - $HOME/.gradle/caches/
+    - $HOME/.gradle/wrapper/
+    - $HOME/.android/build-cache
+