Here is a small method to update static vendored files:

# requires faraday gem to be loaded
#
# @param [Hash] mappings in the format {'url' => 'path_and_filename'}
def install_assets(mappings)
  mappings.each_pair do |url, path|
    resp = Faraday.get url

    unless resp.status == 200
      log = Logger.new(STDERR)
      log.warn "something went wrong? status = #{resp.status}"
      next
    end

    File.open path, 'w' do |f|
      f.write resp.body
    end
  end
end

It can be used in a rake task like this:

namespace :vendor do
  desc 'update vendored assets'
  task :install do
    mappings = {
        'https://raw.github.com/rweng/jquery-thingy-picker/master/less/jquery-thingy-picker.less' =>
            File.expand_path('vendor/assets/stylesheets/jquery-thingy-picker.less', Rails.root),
        'https://raw.github.com/rweng/jquery-thingy-picker/master/javascript/jquery-thingy-picker.js' =>
            File.expand_path('vendor/assets/javascripts/jquery-thingy-picker.js', Rails.root),

    }

    install_assets mappings
  end
end