Use Retrolab on Binder

.binder/environment.yml

@@ -4,6 +4,7 @@ channels:
 dependencies:
   - yarn
   - numpy
-  - jupyterlab>=3
+  - jupyterlab>=3,<4
+  - retrolab
   - matplotlib-base>=2.2.2
   - jupyter-packaging=0.7

.github/workflows/binder-on-pr.yml

@@ -19,7 +19,7 @@ jobs:
             issue_number: context.issue.number,
             owner: context.repo.owner,
             repo: context.repo.repo,
-            body: `[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/${PR_HEAD_USERREPO}/${PR_HEAD_REF}?urlpath=lab/tree/) :point_left: Launch a binder notebook on branch _${PR_HEAD_USERREPO}/${PR_HEAD_REF}_`
+            body: `[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/${PR_HEAD_USERREPO}/${PR_HEAD_REF}?urlpath=retro/notebooks/examples/ipympl.ipynb) :point_left: Launch a binder notebook on branch _${PR_HEAD_USERREPO}/${PR_HEAD_REF}_`
           })
       env:
         PR_HEAD_REF: ${{ github.event.pull_request.head.ref }}

README.md

@@ -4,7 +4,7 @@
 [![Latest PyPI version](https://img.shields.io/pypi/v/ipympl?logo=pypi)](https://pypi.python.org/pypi/ipympl)
 [![Latest conda-forge version](https://img.shields.io/conda/vn/conda-forge/ipympl?logo=conda-forge)](https://anaconda.org/conda-forge/ipympl)
 [![Latest npm version](https://img.shields.io/npm/v/jupyter-matplotlib?logo=npm)](https://www.npmjs.com/package/jupyter-matplotlib)
-[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/matplotlib/ipympl/stable?urlpath=%2Flab%2Ftree%2Fexamples%2Fipympl.ipynb)
+[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/matplotlib/ipympl/stable?urlpath=retro/notebooks/examples/ipympl.ipynb)
 [![Gitter](https://img.shields.io/badge/gitter-Join_chat-blue?logo=gitter)](https://gitter.im/jupyter-widgets/Lobby)
 
 Leveraging the Jupyter interactive widgets framework, `ipympl` enables the interactive features of matplotlib in the Jupyter notebook and in JupyterLab.