Add ruby 2.2 to travis

and allow failure on ruby head

Conflicts:
	.travis.yml

.travis.yml

@@ -2,6 +2,8 @@ rvm:
   - 1.9
   - 2.0
   - 2.1
+  - 2.2
+  - ruby-head
   - jruby-19mode
   - jruby-head
   - rbx-2
@@ -9,6 +11,7 @@ matrix:
   allow_failures:
     - rvm: rbx-2
     - rvm: jruby-head
+    - rvm: ruby-head
 
 script: "rake test"