Test adding black to CI/CD

.drone.yml

@@ -12,3 +12,8 @@ steps:
     image: python:3.9-slim
     commands:
       - python test.py
+
+  - name: black
+    image: pyfound/black:21.7b0
+    commands:
+      - black --check --diff --quiet .

pyproject.toml

@@ -4,3 +4,7 @@ requires = [
     "wheel"
 ]
 build-backend = "setuptools.build_meta"
+
+[tool.black]
+line-length = 79
+target-version = ["py38"]