Add Black

[kclowes]

• Version: v6
• Python: 3.7+
• OS: osx/linux/win

What was wrong?

Want to add black linting to codebase for consistency

How can it be fixed?

Add correct path to black command in tox.ini, and run black on the directory.

Places left to add:

• middleware/
• providers/
• scripts/
• tools/
• utils/
• constants.py
• contract.py
• datastructures.py
• eth.py
• exceptions.py
• geth.py
• iban.py
• logs.py
• main.py
• manager.py
• method.py
• module.py
• net.py
• parity.py
• pm.py
• py.typed
• testing.py
• types.py
• version.py