fix some sync error while using python3

Change-Id: I70925e48756c356d48359679d8ad1b9e33a68595
diff --git a/git_config.py b/git_config.py
index 7bc6f77..70b22ce 100644
--- a/git_config.py
+++ b/git_config.py
@@ -306,7 +306,9 @@
     d = self._do('--null', '--list')
     if d is None:
       return c
-    for line in d.decode('utf-8').rstrip('\0').split('\0'):
+    if not is_python3():
+      d = d.decode('utf-8')
+    for line in d.rstrip('\0').split('\0'):
       if '\n' in line:
         key, val = line.split('\n', 1)
       else: