5.2.4 Changelog missing on readthedocs

[adamchainz]

I found the changelog notes by comparing the GitHub releases ( https://github.com/jupyter/jupyter_client/compare/5.2.3..5.2.4 ), but it seems the change to the file is not on the master branch, only 5.x, and this might be what is stopping them from rendering on ReadTheDocs at https://jupyter-client.readthedocs.io/en/latest/changelog.html.