Bump notebook from 6.0.3 to 6.4.1 in /tutorials

Bumps [notebook](http://jupyter.org) from 6.0.3 to 6.4.1.

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

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

Author: dependabot[bot]

tutorials/requirements.txt

@@ -28,7 +28,7 @@ matplotlib==3.2.1
 mistune==0.8.4
 nbconvert==5.6.1
 nbformat==5.0.4
-notebook==6.0.3
+notebook==6.4.1
 numpy==1.18.2
 open3d==0.9.0.0
 pandas==1.0.3