Add codecov badage in the readme file

README.md

@@ -3,6 +3,7 @@
 [![](http://img.shields.io/badge/godoc-reference-5272B4.svg?style=flat-square)](https://godoc.org/github.com/linuxsuren/http-downloader)
 [![Codacy Badge](https://app.codacy.com/project/badge/Grade/7cc20ea84e0543068c320e471bde560e)](https://www.codacy.com/gh/LinuxSuRen/http-downloader/dashboard?utm_source=github.com&utm_medium=referral&utm_content=LinuxSuRen/http-downloader&utm_campaign=Badge_Grade)
 [![Codacy Badge](https://app.codacy.com/project/badge/Coverage/7cc20ea84e0543068c320e471bde560e)](https://www.codacy.com/gh/LinuxSuRen/http-downloader/dashboard?utm_source=github.com&utm_medium=referral&utm_content=LinuxSuRen/http-downloader&utm_campaign=Badge_Coverage)
+[![codecov](https://codecov.io/gh/LinuxSuRen/http-downloader/branch/master/graph/badge.svg?token=Ntc8z2iEQ2)](https://codecov.io/gh/LinuxSuRen/http-downloader)
 [![Contributors](https://img.shields.io/github/contributors/linuxsuren/http-downloader.svg)](https://github.com/linuxsuren/github-go/graphs/contributors)
 [![GitHub release](https://img.shields.io/github/release/linuxsuren/http-downloader.svg?label=release)](https://github.com/linuxsuren/github-go/releases/latest)
 ![GitHub All Releases](https://img.shields.io/github/downloads/linuxsuren/http-downloader/total)