Update version for CVE-2017-1000460

Looking closer at the fixing version, the respective change to check the
return value is already fixed with the import of 3.1.1:

https://anonscm.debian.org/git/pkg-multimedia/ffmpeg.git/commit/?id=c1a7bf0ae231d5bdcd001fb679f43e4e3f655e9d

Note for reviewers: please double-check for correctness.