updated docs to reflect version update [ci skip]

README.md

@@ -67,7 +67,7 @@ Instructions on how to start GitLab and how to run the tests can be found in the
 GitLab is a Ruby on Rails application that runs on the following software:
 
 - Ubuntu/Debian/CentOS/RHEL
-- Ruby (MRI) 2.1
+- Ruby (MRI) 2.2
 - Git 1.7.10+
 - Redis 2.8+
 - MySQL or PostgreSQL

doc/install/installation.md

@@ -107,7 +107,7 @@ Then select 'Internet Site' and press enter to confirm the hostname.
 
 ## 2. Ruby
 
-_**Note:** The current supported Ruby versions are 2.1.x. Ruby 2.2 and 2.3 are
+_**Note:** The current supported Ruby version is 2.2.x. Ruby 2.3 is
 currently not supported._
 
 The use of Ruby version managers such as [RVM], [rbenv] or [chruby] with GitLab

doc/install/requirements.md

@@ -32,8 +32,7 @@ Please consider using a virtual machine to run GitLab.
 
 ## Ruby versions
 
-GitLab requires Ruby (MRI) 2.1.x and currently does not work with versions 2.2
-and 2.3.
+GitLab requires Ruby (MRI) 2.2.x and currently does not work with version 2.3.
 
 You will have to use the standard MRI implementation of Ruby.
 We love [JRuby](http://jruby.org/) and [Rubinius](http://rubini.us/) but GitLab