Update checkedeps.py rules in DEPS.

Add allow-rules as well in addition to the
disallow-rule in r7014.

BUG=
TBR=tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/14279005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7020 4adac7df-926f-26a2-2b94-8c16560cd09d