Remove backer badge.

README.md

@@ -3,7 +3,6 @@ Casbin
 
 [![Go Report Card](https://goreportcard.com/badge/github.com/casbin/casbin)](https://goreportcard.com/report/github.com/casbin/casbin)
 [![Build Status](https://travis-ci.org/casbin/casbin.svg?branch=master)](https://travis-ci.org/casbin/casbin)
-[![Backers on Open Collective](https://opencollective.com/casbin/backers/badge.svg)](#backers) [![Sponsors on Open Collective](https://opencollective.com/casbin/sponsors/badge.svg)](#sponsors) [![Coverage Status](https://coveralls.io/repos/github/casbin/casbin/badge.svg?branch=master)](https://coveralls.io/github/casbin/casbin?branch=master)
 [![Godoc](https://godoc.org/github.com/casbin/casbin?status.svg)](https://godoc.org/github.com/casbin/casbin)
 [![Release](https://img.shields.io/github/release/casbin/casbin.svg)](https://github.com/casbin/casbin/releases/latest)
 [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/casbin/lobby)
@@ -242,14 +241,12 @@ https://casbin.org/docs/en/adopters
 This project exists thanks to all the people who contribute. 
 <a href="https://github.com/casbin/casbin/graphs/contributors"><img src="https://opencollective.com/casbin/contributors.svg?width=890&button=false" /></a>
 
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 ## Backers
 
 Thank you to all our backers! 🙏 [[Become a backer](https://opencollective.com/casbin#backer)]
 
 <a href="https://opencollective.com/casbin#backers" target="_blank"><img src="https://opencollective.com/casbin/backers.svg?width=890"></a>
 
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 ## Sponsors
 
 Support this project by becoming a sponsor. Your logo will show up here with a link to your website. [[Become a sponsor](https://opencollective.com/casbin#sponsor)]
@@ -265,8 +262,6 @@ Support this project by becoming a sponsor. Your logo will show up here with a l
 <a href="https://opencollective.com/casbin/sponsor/8/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/8/avatar.svg"></a>
 <a href="https://opencollective.com/casbin/sponsor/9/website" target="_blank"><img src="https://opencollective.com/casbin/sponsor/9/avatar.svg"></a>
 
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 ## License
 
 This project is licensed under the [Apache 2.0 license](LICENSE).