Add black command to makefile and black dependency to setup.py

Makefile

@@ -5,7 +5,7 @@ help:
 
 .PHONY: install-dev ## Install development dependencies
 install-dev:
-	pip install -e ".[test]"
+	pip install -e ".[dev]"
 
 test:
 	py.test graphene examples tests_asyncio
@@ -17,3 +17,7 @@ docs: install-dev
 .PHONY: docs-live ## Generate docs with live reloading
 docs-live: install-dev
 	cd docs && make install && make livehtml
+
+.PHONY: format
+format:
+	black graphene examples setup.py tests_asyncio

setup.py

@@ -59,6 +59,8 @@ tests_require = [
     "iso8601",
 ]
 
+dev_requires = ["black==19.3b0", "flake8==3.7.7"] + tests_require
+
 setup(
     name="graphene",
     version=version,
@@ -85,6 +87,6 @@ setup(
         "aniso8601>=6,<9",
     ],
     tests_require=tests_require,
-    extras_require={"test": tests_require},
+    extras_require={"test": tests_require, "dev": dev_requires},
     cmdclass={"test": PyTest},
 )