danger-rcov
This plugin will provide an interface similar to codecov.

Installation
$ gem install danger-rcov
Usage
Inside your Dangerfile:
    markdown rcov.report(
      current_url: "https://circleci.com/api/v1.1/project/github/#{ENV['CIRCLE_PROJECT_USERNAME']}/#{ENV['CIRCLE_PROJECT_REPONAME']}/#{ENV['CIRCLE_BUILD_NUM']}/artifacts?circle-token=#{ENV['CIRCLE_TOKEN']}",
      master_url: "https://circleci.com/api/v1.1/project/github/#{ENV['CIRCLE_PROJECT_USERNAME']}/#{ENV['CIRCLE_PROJECT_REPONAME']}/latest/artifacts?circle-token=#{ENV['CIRCLE_TOKEN']}&branch=master",
      warning: true # this will warn when the code coverage decrease!
    )