Improve travis caching

Author: raphaelm

.travis.yml

@@ -16,6 +16,11 @@ script:
     - git submodule update --init
     - cd pretixdroid
     - TERM=dumb ./gradlew checkDebug lintDebug assembleDebug
+before_cache:
+  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
+  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
 cache:
-    directories:
-        - $HOME/.gradle
+  directories:
+    - $HOME/.gradle/caches/
+    - $HOME/.gradle/wrapper/
+