Travis makes us work harder now to actually get OpenJDK 6

SethTisue · SethTisue · commit e0ac07624863 · 2017-10-19T13:50:04.000-05:00
as per: travis-ci/travis-ci#8199 (comment)
diff --git a/.travis.yml b/.travis.yml
@@ -9,6 +9,11 @@ cache:
 
 language: scala
 
+addons:
+  apt:
+    packages:
+      - openjdk-6-jdk
+
 jdk:
   - openjdk6
   - oraclejdk8
