Kill lock files in cache.

.travis.yml

@@ -10,7 +10,7 @@ jdk:
   - openjdk6
 # Caching for Gradle files, prevents hitting Maven too much.
 before_cache:
-  - rm -f $HOME/.gradle/caches/modules-2/modules-2.lock
+  - find $HOME/.gradle/ -name '*.lock' -print -exec 'rm -f {} \;'
 cache:
   directories:
     - $HOME/.gradle/caches/