Remove astray comma

There's an extra "," at the end of the line, which is causing
trouble when the manifest file specifies a revision for a
project.  Since the default manifest file doesn't specify
revisions for the projects, the problem has gone unnoticed.

Thanks to Barry Silverman <barry@disus.com> for spotting the
issue and providing a patch.

Signed-off-by: Marcelo E. Magallon <marcelo.magallon@gmail.com>

project.py

@@ -940,7 +940,7 @@ class Project(object):
       ref = R_M + self.manifest.branch
 
       if IsId(self.revision):
-        dst = self.revision + '^0',
+        dst = self.revision + '^0'
         self.bare_git.UpdateRef(ref, dst, message = msg, detach = True)
       else:
         remote = self.GetRemote(self.remote.name)