Adjust dependencies for older Rubies

Gemfile

@@ -7,6 +7,7 @@ group :development do
     gem 'test-unit'
   else
     gem 'minitest', '< 5.0'
+    gem 'listen', '~>3.0.0'
   end
 
   gem 'rake'
@@ -14,7 +15,6 @@ group :development do
   gem 'shoulda', '~> 3.5'
   gem 'cucumber', '1.3.11'
   gem 'redcarpet'
-  gem 'launchy', '~> 2.3'
 
   gem 'unicode_utils'