Bump jupyterlab from 1.0.4 to 1.2.21

Bumps [jupyterlab](https://github.com/jupyterlab/jupyterlab) from 1.0.4 to 1.2.21.
- [Release notes](https://github.com/jupyterlab/jupyterlab/releases)
- [Changelog](https://github.com/jupyterlab/jupyterlab/blob/master/CHANGELOG.md)
- [Commits](https://github.com/jupyterlab/jupyterlab/commits)

---
updated-dependencies:
- dependency-name: jupyterlab
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -24,7 +24,7 @@ json5==0.8.5
 jsonschema==3.0.2
 jupyter-client==5.3.1
 jupyter-core==4.5.0
-jupyterlab==1.0.4
+jupyterlab==1.2.21
 jupyterlab-server==1.0.0
 kiwisolver==1.1.0
 MarkupSafe==1.1.1