Simplify JRuby entry on travis

The JRuby env var was being set to all builds on the matrix

Author: abinoam

.travis.yml

@@ -11,7 +11,6 @@ rvm:
   - ruby-2.2.4
   - ruby-2.2.2
   - ruby-2.3.0-preview2
-  - jruby-head
 matrix:
   exclude:
     - os: linux
@@ -24,8 +23,9 @@ matrix:
       rvm: ruby-2.0.0-p648
     - os: osx
       rvm: ruby-2.3.0-preview2
-env:
-  - JRUBY_OPTS="-Xcli.debug=true --debug"
+  include:
+    - rvm: jruby-head
+      env: JRUBY_OPTS="-Xcli.debug=true --debug"
 addons:
   code_climate:
     repo_token: 60d9731d654527cb53aabc7db15bcde87d701ddb6b1cba8fc0da6aba16d00bb1