/usr/lib/go-1.10/favicon.ico.gz is in golang-1.10-doc 1.10.1-1ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/go-1.10/../../share/doc/golang-1.10-doc/favicon.ico.gz
/usr/lib/go-1.10/../../share/doc/golang-1.10-doc/favicon.ico.gz