Use JDK 8 to fix travis falure for maven test

dapengzhang0 · ejona86 · commit df5a8b342c59 · 2019-08-22T14:48:45.000-07:00
diff --git a/.travis.yml b/.travis.yml
@@ -2,6 +2,9 @@ language: java
 
 sudo: false
 
+jdk:
+  - openjdk8
+
 cache:
   directories:
   - "$HOME/.m2"
