adjust rvm list in .travis.yml

.travis.yml

 language: ruby
 rvm:
 - 2.2.0
-- ruby-2.1.3-p242
+- 2.1.3-p242
 - 2.0.0
 - 1.9.3
-- ruby-1.9.2-p180
-- ruby-1.9.1-p431
-- ruby-1.8.7-p334
+- 1.9.2-p180
+- 1.9.1-p431
+- 1.8.7-p334
 - jruby-1.6.1
-- rbx-head
-- ree-1.8.7-2011.03
+- rbx
+- ree
 install:
 - bundle install
 script: