Bump nbconvert from 5.5.0 to 6.5.1 in /docker-projects/ipython_notebook

Bumps [nbconvert](https://github.com/jupyter/nbconvert) from 5.5.0 to 6.5.1.
- [Release notes](https://github.com/jupyter/nbconvert/releases)
- [Commits](jupyter/nbconvert@5.5...6.5.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

docker-projects/ipython_notebook/requirements.txt

@@ -20,7 +20,7 @@ kiwisolver==1.1.0
 MarkupSafe==1.1.1
 matplotlib==3.1.1
 mistune==0.8.4
-nbconvert==5.5.0
+nbconvert==6.5.1
 nbformat==4.4.0
 notebook==6.4.1
 numpy==1.16.4