Hotfix/dependency update (#1249)

* Update README.md

Make imcompatibility to jupyterlab 4 explicit

* Ignore package.json for prettify

* Apply suggestions from code review

---------

Co-authored-by: Frédéric Collonval <fcollonval@gmail.com>
Co-authored-by: Frédéric Collonval <fcollonval@users.noreply.github.com>

Author: mfakaehler

README.md

@@ -13,7 +13,7 @@ To see the extension in action, open the example notebook included in the Binder
 
 ## Requirements
 
-- JupyterLab >= 3.0 ([older version](https://github.com/jupyterlab/jupyterlab-git/tree/jlab-2) available for 2.x)
+- JupyterLab >= 3.0, < 4 ([older version](https://github.com/jupyterlab/jupyterlab-git/tree/jlab-2) available for 2.x)
 - Git (version `>=2.x`)
 
 ## Usage