message: [ci] show code coverage
  Closes:
  Approved by: sausagee
diff: [![CircleCI](https://circleci.com/gh/libra/libra.svg?style=shield)](https://circleci.com/gh/libra/libra)
  [![License](https://img.shields.io/badge/license-Apache-green.svg)](LICENSE)
  +[![codecov](https://codecov.io/gh/libra/libra/branch/master/graph/badge.svg)](https://codecov.io/gh/libra/libra)
  Libra Core implements a decentralized, programmable database which provides a financial infrastructure that can empower billions of people.
  