Gemfile: Berkshelf => 1.4.0

Gemfile

@@ -4,7 +4,7 @@
 source 'https://rubygems.org'
 
 gem 'vagrant' #, :git => 'git://github.com/mitchellh/vagrant.git', :branch => 'v1.2.2'
-gem 'berkshelf', '~> 1.4.0'
+gem 'berkshelf', '>= 1.4.0'
 gem 'test-kitchen', '~> 1.0.0.alpha.0'
 gem 'kitchen-vagrant', '~> 0.10.0'