dev-python/mypy: add mypy 0.781 from upstream gentoo

Copied from https://github.com/gentoo/gentoo.git at commit
82f12930ff6f90b237815b66a2dc93960bac9182 with KEYWORDS replaced with
"*".

BUG=b:162009542
TEST=sudo emerge mypy

Change-Id: I7200b5be1f5e8348633d8d02906f54df10bc54fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/2316395
Tested-by: Tom Hughes <tomhughes@chromium.org>
Auto-Submit: Tom Hughes <tomhughes@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Tom Hughes <tomhughes@chromium.org>
3 files changed