Fix reitveld base URL for googlesource.com repos.
Fix reitveld base URL for googlesource.com repos.

The base url was previously being generated as
URL@BRANCH.  I'm not sure if this works anywhere
but it certainly doesn't on googlesource.com.
Here we want URL/+/BRANCH.

R=iannucci@chromium.org, sergeyberezin@chromium.org

Review URL: https://codereview.chromium.org/652193004

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@292493 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools