update .travis.yml for jruby9k jobs

Author: ph

.travis.yml

@@ -1,10 +1,17 @@
 ---
 sudo: false
 jdk:
-  - oraclejdk8
+- oraclejdk8
 language: ruby
 cache: bundler
 rvm:
-  - jruby-1.7.25
+- jruby-1.7.25
 script:
-  - bundle exec rspec spec
+- bundle exec rspec spec
+matrix:
+  include:
+  - rvm: jruby-9.1.10.0
+    env: LOGSTASH_BRANCH=master
+  - rvm: jruby-1.7.25
+    env: LOGSTASH_BRANCH=5.x
+  fast_finish: true