Grant dererk arm repo access

Dererk has taken over making the arm debs so it would be nice for him to have commit access to the packaging branch [1] so he can update it himself. Looking back through trac it looks like we've never made him ldap credentials - Dererk, please provide... name (first/middle/last): preferred username: forwarding email address: pgp key fingerprint:

example: https://trac.torproject.org/projects/tor/ticket/3191

Cheers! -Damian

[1] https://gitweb.torproject.org/arm.git/tree/packaging:/build/debian