Adds Sprockets Directive `depend_on_config`. I'm using this to load .yml locale translations on the server into the client in json

0. sprockets_depend_on_config.rb

=begin

  Useage:
  
  #assets/locales/en.js.erb
  ```js
    //= depend_on_config 'locales/es.yml'
  ```
=end

class Sprockets::DirectiveProcessor
  def process_depend_on_config_directive(file)
    path = File.expand_path(file, "#{Rails.root}/config")
    context.depend_on(path)
  end
end

1. js_locale_helper.rb

module JsLocaleHelper

  def self.output_locale(locale)
    locale_str = locale.to_s
    file       = Rails.root.join("config/locales/", "#{locale_str}.yml")
    YAML::load(File.open file)[locale_str].to_json.html_safe
  end

end

2. en.js.erb

//= depend_on_config 'locales/es.yml'

I18n.translations = I18n.translations || {};
I18n.translations.en = "<%= JsLocaleHelper.output_locale(:en) %>"

3. en.yml

en:
  hello: Hello World

Which version of sprockets are you using? This seems to blow up on sprockets 3.4.

undefined local variable or method context' for #Sprockets::DirectiveProcessor:0x007fe27be37280`