Error While installing rails, i18n requires Ruby version >= 1.9.3

I am working on a project that requires Ruby Version 1.8.7 and Rails 3.1.1. Now, Ruby was installed fine but rails is throwing an error. Here is the command that I used to install rails gem install rails --version '3.1.1' I have used rvm to install ruby.

ERROR: Error installing rails: i18n requires Ruby version >= 1.9.3.

This is the error am getting. Can someone please help. Thank you in advance.