kill off rbx and jruby from the build matrix, as they always fail and it just wastes travis resources.

Author: mceachen

.travis.yml

@@ -5,8 +5,9 @@ rvm:
   - 2.3.1
   - 2.2.5
   - 2.0
-  - jruby-head
-  - rbx
+# these haven't been passing for a while:
+#  - jruby-head
+#  - rbx
 
 gemfile:
   - gemfiles/activerecord_4.1.gemfile