[Java] Update travis build.

Author: mjpt777

.travis.yml

@@ -1,4 +1,3 @@
-language: cpp
 
 sudo: false
 
@@ -99,5 +98,14 @@ before_script:
   - export CXX=$COMPILER
   - ./gradlew
 
+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/
+
 script:
   - ./cppbuild/cppbuild