Bump nbconvert from 6.4.0 to 6.5.1 in /ncli (#4018)

Bumps [nbconvert](https://github.com/jupyter/nbconvert) from 6.4.0 to 6.5.1.
- [Release notes](https://github.com/jupyter/nbconvert/releases)
- [Commits](https://github.com/jupyter/nbconvert/compare/6.4.0...6.5.1)

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

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ncli/requirements.txt

@@ -39,7 +39,7 @@ matplotlib-inline==0.1.3
 mistune==2.0.3
 mypy-extensions==0.4.3
 nbclient==0.5.10
-nbconvert==6.4.0
+nbconvert==6.5.1
 nbformat==5.1.3
 nest-asyncio==1.5.4
 networkx==2.6.3