git: use the correct type for stopping changelog.revs()

The `tip` function returns a binary node, but the database is expecting an int.

Differential Revision: https://phab.mercurial-scm.org/D10525

hgext/git/gitlog.py

@@ -147,7 +147,7 b' class changelog(baselog):'
 
     def revs(self, start=0, stop=None):
         if stop is None:
-            stop = self.tip()
+            stop = self.tiprev()
         t = self._db.execute(
             'SELECT rev FROM changelog '
             'WHERE rev >= ? AND rev <= ? '