Bump notebook from 6.1.4 to 6.1.5 in /examples/lxmert (#86)

Bumps [notebook](https://github.com/jupyter/jupyterhub) from 6.1.4 to 6.1.5.
- [Release notes](https://github.com/jupyter/jupyterhub/releases)
- [Changelog](https://github.com/jupyterhub/jupyterhub/blob/master/CHECKLIST-Release.md)
- [Commits](https://github.com/jupyter/jupyterhub/commits)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

examples/lxmert/requirements.txt

@@ -47,7 +47,7 @@ nbclient==0.5.0
 nbconvert==6.0.1
 nbformat==5.0.7
 nest-asyncio==1.4.0
-notebook==6.1.4
+notebook==6.1.5
 numpy==1.19.2
 opencv-python==4.4.0.42
 packaging==20.3