typo fix

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>

master/buildbot/master.py

@@ -456,7 +456,7 @@ def addBuildset(self, scheduler, **kwargs):
     # state maintenance (private)
     def getObjectId(self):
         """
-        Return the obejct id for this master, for associating state with the
+        Return the object id for this master, for associating state with the
         master.
 
         @returns: ID, via Deferred