lib/pliny/router.rb
def version(*versions, &block)
      condition = lambda { |env|
        versions.include?(env["HTTP_X_API_VERSION"])
      }
      with_conditions(condition, &block)
    end
def version(*versions, &block)
      condition = lambda { |env|
        versions.include?(env["HTTP_X_API_VERSION"])
      }
      with_conditions(condition, &block)
    end
yield to a builder block in which all defined apps will only respond for
 the given version