Require Ruby 2.1

README.md

@@ -124,7 +124,7 @@ during installation.
 1. A non-root Unix user, this can be your normal user but **DO NOT** run the
    installation as a root user
-2. Ruby 2.1.8 or newer installed with a Ruby version manager (RVM, rbenv,
+2. Ruby 2.1 (2.1.8 or newer) installed with a Ruby version manager (RVM, rbenv,
    chruby, etc.), **DO NOT** use the system Ruby
 3. Bundler, which you can install with `gem install bundler`