fix code of conduct file name

README.md

@@ -11,7 +11,7 @@
 [![Coverity](https://scan.coverity.com/projects/1038/badge.svg)](https://scan.coverity.com/projects/grass)
 [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.5176030.svg)](https://doi.org/10.5281/zenodo.5176030)
 [![Join the chat at https://gitter.im/grassgis/community](https://badges.gitter.im/grassgis/community.svg)](https://gitter.im/grassgis/community?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](code_of_conduct.md)
+[![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](CODE_OF_CONDUCT.md)
 
 ## Description