Bump notebook in /docs/samples/custom/kfserving-custom-model (kubeflo…

…w#1221)

Bumps [notebook](https://github.com/jupyter/jupyterhub) from 6.0.3 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)

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

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

docs/samples/custom/kfserving-custom-model/requirements.txt

@@ -41,7 +41,7 @@ minio==5.0.7
 mistune==0.8.4
 nbconvert==5.6.1
 nbformat==5.0.4
-notebook==6.0.3
+notebook==6.1.5
 numpy==1.18.1
 oauthlib==3.1.0
 pandocfilters==1.4.2