Make postrm script executable
Make postrm script executable

This breaks the .deb build on Omnibus 4.0.0

aleksandrs-ledovskis/omnibus-gitlab,aleksandrs-ledovskis/omnibus-gitlab,aleksandrs-ledovskis/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,gitlabhq/omnibus-gitlab,felixbuenemann/omnibus-gitlab,felixbuenemann/omnibus-gitlab,copystudy/omnibus-gitlab,copystudy/omnibus-gitlab,felixbuenemann/omnibus-gitlab,copystudy/omnibus-gitlab,gitlabhq/omnibus-gitlab