devel/libepoll-shim: update to 0.0.20201229

Fixes VAAPI in www/firefox >= 78.0 on FreeBSD >= 13.0

Changes: https://github.com/jiixyj/epoll-shim/compare/3840e9c...1c27d2d
Approved by: bapt, manu
Differential Revision: https://reviews.freebsd.org/D27965