python black missing aiohttp dependency for blackd daemon mode

[abathur]

Issue description

A few months back black added a new command blackd for running black in a persistent daemon/server mode, bit this adds an additional dependency on python package aiohttp

Steps to reproduce

[13:14:57] ~$
nix-shell --pure -p python3Packages.black

[nix-shell:~]$ blackd
Traceback (most recent call last):
  File "/nix/store/mzilvwc55cz9hz8vrisd68m6mqc3gdd6-python3.7-black-18.9b0/bin/.blackd-wrapped", line 8, in <module>
    from blackd import main
  File "/nix/store/mzilvwc55cz9hz8vrisd68m6mqc3gdd6-python3.7-black-18.9b0/lib/python3.7/site-packages/blackd.py", line 6, in <module>
    from aiohttp import web
ModuleNotFoundError: No module named 'aiohttp'

Technical details

• system: "x86_64-darwin"
• host os: Darwin 18.2.0, macOS 10.14.2
• multi-user?: no
• sandbox: no
• version: nix-env (Nix) 2.1.3
• channels(abathur): "darwin, nixpkgs-19.03pre165281.7d864c6bd63"
• nixpkgs: /Users/abathur/.nix-defexpr/channels/nixpkgs