Added RBX to the build matrix.

Let's run the tests with RBX 3 as well :)

Author: Omer Katz

.travis.yml

@@ -13,6 +13,7 @@ rvm:
   - jruby-9.0.5.0
   - jruby-head
   - rbx-2
+  - rbx
 
 jdk:
   - oraclejdk8
@@ -33,6 +34,7 @@ matrix:
     - rvm: jruby-head
     - rvm: 1.9.3
     - rvm: rbx-2
+    - rvm: rbx
     - rvm: jruby-head
       jdk: oraclejdk8
       env: TRUFFLE=1