multimedia/ffmpeg: update to 4.0.1
Changes: https://git.ffmpeg.org/gitweb/ffmpeg.git/blob/n4.0.1:/Changelog
ABI: https://abi-laboratory.pro/tracker/timeline/ffmpeg/
Security: CVE-2018-12458, CVE-2018-12459, CVE-2018-12460
PR: 227726 (for tracking)