Bump supervisor from 4.0.3 to 4.0.4 in /{{cookiecutter.app_name}} (#521)

Bumps [supervisor](https://github.com/Supervisor/supervisor) from 4.0.3 to 4.0.4.
- [Release notes](https://github.com/Supervisor/supervisor/releases)
- [Changelog](https://github.com/Supervisor/supervisor/blob/master/CHANGES.rst)
- [Commits](https://github.com/Supervisor/supervisor/compare/4.0.3...4.0.4)

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

{{cookiecutter.app_name}}/Pipfile

@@ -23,7 +23,7 @@ WTForms = "==2.2.1"
 # Deployment
 gevent = "==1.4.0"
 gunicorn = ">=19.1.1"
-supervisor = "==4.0.3"
+supervisor = "==4.0.4"
 
 # Webpack
 flask-webpack = "==0.1.0"