use rack 1.6.4

Author: Charlie Somerville

Gemfile

@@ -3,7 +3,7 @@ source 'https://rubygems.org'
 gemspec
 
 gem "rake"
-gem "rack"
+gem "rack", "1.6.4"
 gem "rspec", "2.14.1"
 gem "binding_of_caller", platforms: :ruby
 gem "pry", "0.9.12"