Make travis cache gradle dependencies

Author: Runemoro

.travis.yml

@@ -3,6 +3,14 @@ notifications:
   email: false
 if: tag IS blank
 
+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/
+
 before_install: chmod +x gradlew
 install: "./gradlew setupCIWorkspace"
 script: "./gradlew clean build"