Update all references to Review Board 2.1 to say 2.5 instead.

Review Request #7074 — Created March 17, 2015 and submitted — Latest diff uploaded

Information

Review Board
master
81b4413...

Reviewers

We decided a while back that the next major release of Review Board
would be 2.5, but we still had many bits of documentation stating 2.1
instead. This updates all those for the proper version.

Grepped through the codebase. Didn't see any more references.