fix: CI badge appears twice in readme (#8689)

Author: robertylewis

README.md

@@ -1,6 +1,5 @@
 # mathlib4
 
-![](https://github.com/leanprover-community/mathlib4/workflows/continuous%20integration/badge.svg?branch=master)
 ![GitHub CI](https://github.com/leanprover-community/mathlib4/workflows/continuous%20integration/badge.svg?branch=master)
 [![Bors enabled](https://bors.tech/images/badge_small.svg)](https://mathlib-bors-ca18eefec4cb.herokuapp.com/repositories/16)
 [![project chat](https://img.shields.io/badge/zulip-join_chat-brightgreen.svg)](https://leanprover.zulipchat.com)