Bump the minimal required version of docker and remove dependency on six

pyproject.toml

@@ -17,11 +17,8 @@ classifiers = [
 python = "^3.7"
 pytest = ">=5.0"
 requests = ">=2.22.0"
-docker = ">=4.2.0"
+docker = ">=5.0.3"
 typing_extensions = ">=3.7.4"
-# docker==5.0 needs six but doesn't require it as a dependency
-# https://github.com/docker/docker-py/issues/2842
-six = ">=1.15.0"
 
 [tool.poetry.dev-dependencies]
 flake8 = ">=3.7.7"