Specify Version Requirements for Bourbon and Neat

This resolves a sass version requirement conflict with sass-rails. These version
requirements should be removed or updated once sass-rails supports sass 3.3.

This pull request closes #328 on https://github.com/thoughtbot/suspenders.

templates/Gemfile.erb

@@ -3,14 +3,14 @@ source 'https://rubygems.org'
 ruby '<%= RUBY_VERSION %>'
 
 gem 'airbrake'
-gem 'bourbon'
+gem 'bourbon', '~> 3.2.1'
 gem 'coffee-rails'
 gem 'delayed_job_active_record'
 gem 'email_validator'
 gem 'flutie'
 gem 'high_voltage'
 gem 'jquery-rails'
-gem 'neat'
+gem 'neat', '~> 1.5.1'
 gem 'pg'
 gem 'rack-timeout'
 gem 'rails', '~> 4.1.0'