Fix link to Code of Conduct in CONTRIBUTING.md (#7758)

Updated the link to Project Jupyter's Code of Conduct to fix the CI check.

Author: jtpio

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 Thanks for contributing to Jupyter Notebook!
 
-Make sure to follow [Project Jupyter's Code of Conduct](https://github.com/jupyter/governance/blob/master/conduct/code_of_conduct.md)
+Make sure to follow [Project Jupyter's Code of Conduct](https://jupyter.org/governance/conduct/code-of-conduct)
 for a friendly and welcoming collaborative environment.
 
 ## Setting up a development environment