Bump notebook from 6.0.1 to 6.4.12

Bumps [notebook](http://jupyter.org) from 6.0.1 to 6.4.12.

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

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

requirements.txt

@@ -33,7 +33,7 @@ mistune==0.8.4
 mlxtend==0.17.0
 nbconvert==6.5.1
 nbformat==4.4.0
-notebook==6.0.1
+notebook==6.4.12
 numpy==1.17.2
 pandas==0.25.1
 pandocfilters==1.4.2