set default file encoding to utf-8

There's no reason to support any other encoding in these files.
This only affects the files themselves and not streams they open.

Bug: https://crbug.com/gerrit/10418
Change-Id: I053cb40cd3666ce5c8a0689b9dd938f24ca765bf
diff --git a/repo b/repo
index c4c9786..69c14a8 100755
--- a/repo
+++ b/repo
@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+# -*- coding:utf-8 -*-
 
 # repo default configuration
 #