instance method write_specification

# File railties/lib/rails/gem_dependency.rb, line 263
    def write_specification(spec)
      # copy the gem's specification into GEMDIR/.specification so that
      # we can access information about the gem on deployment systems
      # without having the gem installed
      File.open(unpacked_specification_filename, 'w') do |file|
        file.puts spec.to_yaml
      end
    end