Bump waitress from 1.3.0 to 1.4.0 in /src/app

Bumps [waitress](https://github.com/Pylons/waitress) from 1.3.0 to 1.4.0.
- [Release notes](https://github.com/Pylons/waitress/releases)
- [Changelog](https://github.com/Pylons/waitress/blob/master/CHANGES.txt)
- [Commits](https://github.com/Pylons/waitress/compare/v1.3.0...v1.4.0

)

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

src/app/requirements.txt

@@ -54,7 +54,7 @@ soupsieve==1.9.2
 termcolor==1.1.0
 traitlets==4.3.2
 urllib3==1.25.3
-waitress==1.3.0
+waitress==1.4.0
 wcwidth==0.1.7
 Werkzeug==0.15.4
 zipp==0.5.1