chore(deps-dev): update black requirement from ^18.3-alpha.0 to ^19.3b0

Updates the requirements on [black](https://github.com/ambv/black) to permit the latest version.
- [Release notes](https://github.com/ambv/black/releases)
- [Commits](https://github.com/ambv/black/commits)

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

Author: dependabot-support

pyproject.toml

@@ -54,7 +54,7 @@ tomlkit = "^0.5.3"
 
 [tool.poetry.dev-dependencies]
 ipython = "^7.2"
-black = "^18.3-alpha.0"
+black = "^19.3b0"
 pytest = "^4.0"
 flake8 = "^3.6"
 pytest-cov = "^2.6"