Bump environs from 4.2.0 to 5.1.0 in /{{cookiecutter.app_name}} (#518)

Bumps [environs](https://github.com/sloria/environs) from 4.2.0 to 5.1.0.
- [Release notes](https://github.com/sloria/environs/releases)
- [Changelog](https://github.com/sloria/environs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sloria/environs/compare/4.2.0...5.1.0)

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

{{cookiecutter.app_name}}/Pipfile

@@ -39,7 +39,7 @@ Flask-Caching = ">=1.0.0"
 Flask-DebugToolbar = "==0.10.1"
 
 # Environment variable parsing
-environs = "==4.2.0"
+environs = "==5.1.0"
 
 [dev-packages]
 # Testing