Add openjdk6 support

vintagewang · vintagewang · commit 7137aaff172f · 2017-08-16T15:02:24.000+08:00
diff --git a/.travis.yml b/.travis.yml
@@ -2,6 +2,7 @@ language: java
 jdk:
 - oraclejdk8
 - oraclejdk7
+- openjdk6
 
 script: cd code/ && mvn install
 env:
