Bump isort from 4.3.13 to 4.3.15 in /{{cookiecutter.app_name}}

Bumps [isort](https://github.com/timothycrosley/isort) from 4.3.13 to 4.3.15.
- [Release notes](https://github.com/timothycrosley/isort/releases)
- [Changelog](https://github.com/timothycrosley/isort/blob/develop/CHANGELOG.md)
- [Commits](https://github.com/timothycrosley/isort/compare/4.3.13...4.3.15)

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

{{cookiecutter.app_name}}/Pipfile

@@ -56,5 +56,5 @@ flake8-debugger = "==3.1.0"
 flake8-docstrings = "==1.3.0"
 flake8-isort = "==2.6.0"
 flake8-quotes = "==1.0.0"
-isort = "==4.3.13"
+isort = "==4.3.15"
 pep8-naming = "==0.8.2"