on travis test against 5.6 and 6.0 logstash-core

Author: jsvd

.travis.yml

@@ -9,9 +9,11 @@ matrix:
   include:
   - rvm: jruby-9.1.10.0
     env: LOGSTASH_BRANCH=master
+  - rvm: jruby-9.1.10.0
+    env: LOGSTASH_BRANCH=6.x
   - rvm: jruby-1.7.25
-    env: LOGSTASH_BRANCH=5.x
+    env: LOGSTASH_BRANCH=5.6
   fast_finish: true
 install: true
 script: ci/build.sh
-jdk: oraclejdk8
+jdk: oraclejdk8