Change to 2.2.5 instead of 2.2.2

We don't need 2.2.2 exactly, switching to 2.2.5 shaves a solid 30 seconds off build time, as it is preinstalled on travis

site/_docs/continuous-integration.md

@@ -94,7 +94,7 @@ Your `.travis.yml` file should look like this:
 ```yaml
 language: ruby
 rvm:
-- 2.2.2
+- 2.2.5
 
 before_script:
  - chmod +x ./script/cibuild # or do this locally and commit
@@ -127,7 +127,7 @@ access to Bundler, RubyGems, and a Ruby runtime.
 
 ```yaml
 rvm:
-- 2.2.2
+- 2.2.5
 ```
 
 RVM is a popular Ruby Version Manager (like rbenv, chruby, etc). This