Jupyter_core 4.8.0 release candidate

The jupyter_core project has released a release candidate for 4.8.0. Changelog is up at Changes in jupyter-core — jupyter_core 4.8.0rc0 documentation. Install with pip install --pre jupyter_core==4.8.0rc0

Please test and let us know any feedback you may have at 4.8 Release Plan · Issue #235 · jupyter/jupyter_core · GitHub.