Fix 1.9 build.

Author: simi

Gemfile

@@ -3,3 +3,5 @@ source 'https://rubygems.org'
 gemspec
 gem "therubyracer", "~> 0.12.0", :require => nil, :platforms => :ruby
 gem "therubyrhino", "~> 2.0.2", :require => nil, :platforms => :jruby
+
+gem "mime-types", "~> 2.6.2", :platforms => :ruby_19