Make CircleCI badge specific to master branch (#1831)

README.md

@@ -3,7 +3,7 @@
 [![Documentation Status](https://readthedocs.org/projects/esmvaltool/badge/?version=latest)](https://esmvaltool.readthedocs.io/en/latest/?badge=latest)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.3401363.svg)](https://doi.org/10.5281/zenodo.3401363)
 [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/ESMValGroup?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-[![CircleCI](https://circleci.com/gh/ESMValGroup/ESMValTool.svg?style=svg)](https://circleci.com/gh/ESMValGroup/ESMValTool)
+[![CircleCI](https://circleci.com/gh/ESMValGroup/ESMValTool/tree/master.svg?style=svg)](https://circleci.com/gh/ESMValGroup/ESMValTool/tree/master)
 [![Codacy Badge](https://app.codacy.com/project/badge/Coverage/79bf6932c2e844eea15d0fb1ed7e415c)](https://www.codacy.com/gh/ESMValGroup/ESMValTool?utm_source=github.com&utm_medium=referral&utm_content=ESMValGroup/ESMValTool&utm_campaign=Badge_Coverage)
 [![Codacy Badge](https://app.codacy.com/project/badge/Grade/79bf6932c2e844eea15d0fb1ed7e415c)](https://www.codacy.com/gh/ESMValGroup/ESMValTool?utm_source=github.com&utm_medium=referral&utm_content=ESMValGroup/ESMValTool&utm_campaign=Badge_Grade)
 [![Docker Build Status](https://img.shields.io/docker/build/esmvalgroup/esmvaltool.svg)](https://hub.docker.com/r/esmvalgroup/esmvaltool/)