LGTM.com - false positive on __init_subclass__ arguments

[s-knibbs]

The alert states that self should be the first argument of __init_subclass__.

This was added in python 3.6 and is implicitly a classmethod which uses cls as its first argument.

https://lgtm.com/projects/g/s-knibbs/dataclasses-jsonschema/snapshot/0a39c1a41395855d12e92dc498054a9a6bc9a1c6/files/dataclasses_jsonschema/__init__.py?sort=name&dir=ASC&mode=heatmap#x43c1152eb8ec8f3a:1