Don’t bother supporting Rails 3.1.

Rails 3.1 doesn't support `watchable_files` (amongst other things). Also,
I'm assume nobody is actually using react-rails with Rails 3.1 as
there'd probably be a bug report by now.

Author: benpickles

Appraisals

@@ -1,10 +1,3 @@
-appraise "rails-3.1" do
-  gem 'rails', '~> 3.1.12'
-  # Buggy sprockets can break tests under Ruby 2.0. Use a decent version.
-  # See https://github.com/sstephenson/sprockets/issues/352
-  #gem 'sprockets', '>= 2.2.2'
-end
-
 appraise "rails-3.2" do
   gem 'rails', '~> 3.2.21'
 end