Update WebOb version specification

Now that the other projects are using WebOb>=1.2 we can
specify that, too.

See bug #1092227 for details.

Change-Id: Ifcb99354f405d9f4dc113d01d83b2a9d76660fc5
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Merge "Update WebOb version specification"