[ROR] 如何移除較新版本的rails

$ which rails
~/software/bin/rails
$ rails -v
Rails 4.0.0
$ gem list | grep rails
rails (4.0.0, 3.2.13, 3.2.9, 3.2.6)
$ gem uninstall rails -v 4.0.0

You have requested to uninstall the gem:
        rails-4.0.0
figaro-0.7.0 depends on [rails (< 5, >= 3)]
.....
.....
Continue with Uninstall? [Yn]  y
Successfully uninstalled rails-4.0.0
$ gem list | grep rails
rails (3.2.13, 3.2.9, 3.2.6)
$ rails  -v
Rails 4.0.0
$ gem uninstall railties -v 4.0.0

You have requested to uninstall the gem:
        railties-4.0.0
coffee-rails-4.0.0 depends on [railties (< 5.0, >= 4.0.0.beta)]
....
....
If you remove this gems, one or more dependencies will not be met.
Continue with Uninstall? [Yn]  y
Successfully uninstalled railties-4.0.0
$ rails -v
Rails 3.2.13