Try using rbx-2.2.10 as suggested in travis-ci#2542.

dblock · dblock · commit 74eb1a4e4f70 · 2014-07-18T16:09:16.000-04:00
diff --git a/.travis.yml b/.travis.yml
@@ -8,4 +8,4 @@ rvm:
   - 2.0.0
   - 1.9.3
   - jruby-19mode
-  - rbx-2
+  - rbx-2.2.10
