fix travis-ci script.
diff --git a/.travis.yml b/.travis.yml
index cafe93d..ec7c08a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,7 +15,10 @@
 

 language: java

 sudo: false

-

+dist: trusty

+cache:

+  directories:

+    - $HOME/.m2

 jdk:

   - openjdk7

   - oraclejdk7