4.4.0-91.114) is not available, but a newer one is (4.4.0-142.168). We redirected you there.
/usr/share/doc/libmp3lame-dev/changelog.Debian.gz is in libmp3lame-dev 3.100-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libmp3lame-dev/../libmp3lame0/changelog.Debian.gz