mpv: security bump to 0.27.2

Fixes CVE-2018-6360: mpv through 0.28.0 allows remote attackers to execute
arbitrary code via a crafted web site, because it reads HTML documents
containing VIDEO elements, and accepts arbitrary URLs in a src attribute
without a protocol whitelist.

[Peter: Add CVE description]
Signed-off-by: Mahyar Koshkouei <mahyar.koshkouei@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>