Remove microbadger.com (the website is gone)

README.md

@@ -27,7 +27,6 @@ Whatever your use case, `step-ca` is easy to use and hard to misuse, thanks to [
 [Contributor's Guide](./docs/CONTRIBUTING.md)
 
 [![GitHub release](https://img.shields.io/github/release/smallstep/certificates.svg)](https://github.com/smallstep/certificates/releases/latest)
-[![CA Image](https://images.microbadger.com/badges/image/smallstep/step-ca.svg)](https://microbadger.com/images/smallstep/step-ca)
 [![Go Report Card](https://goreportcard.com/badge/github.com/smallstep/certificates)](https://goreportcard.com/report/github.com/smallstep/certificates)
 [![Build Status](https://travis-ci.com/smallstep/certificates.svg?branch=master)](https://travis-ci.com/smallstep/certificates)
 [![License](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](https://opensource.org/licenses/Apache-2.0)