/usr/share/doc/unity-webapps-dev/changelog.Debian.gz is in unity-webapps-dev 2.4.17+15.10.20150616-0ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/unity-webapps-dev/../unity-webapps-common/changelog.Debian.gz