Require travis 'trusty' distribution for JDK 6

See: https://docs.travis-ci.com/user/reference/trusty/#jvm-clojure-groovy-java-scala-images
diff --git a/.travis.yml b/.travis.yml
index 8d829e5..7eaca75 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -16,7 +16,13 @@
 language: java

 sudo: true

 

-dist: xenial

+# Required to build with openjdk6 and 7

+dist: trusty

+

+addons:

+  apt:

+    packages:

+      - openjdk-6-jdk

 

 jdk:

   - openjdk6