Update .travis.yml

Author: pgleeson

.travis.yml

@@ -4,7 +4,6 @@ before_install:
 - sed -i.bak -e 's|https://nexus.codehaus.org/snapshots/|https://oss.sonatype.org/content/repositories/codehaus-snapshots/|g' ~/.m2/settings.xml
 
 jdk:
-  - openjdk6
   - openjdk7
   - oraclejdk7
   - oraclejdk8