ceph-deploy-pull-requests: add Travis to admins list

Travis is a co-maintainer of ceph-deploy; add him to the list of
administrators for the GitHub Pull Requests plugin. Jenkins will trust
any pull requests from Travis and build them automatically.

(I don't know why Jenkins wasn't already trusting Travis since he's a
member of the Ceph organization.)
Merge pull request #24 from ktdreyer/ceph-deploy-pr-trust-throden

ceph-deploy-pull-requests: add Travis to admins list