try slove travis issue

NickNYU · NickNYU · commit a49125e1e044 · 2019-07-23T11:42:07.000+08:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,6 +1,8 @@
 language: java
 jdk:
   - oraclejdk8
+dist:
+  trusty
 cache:
   directories:
       - $HOME/.m2
