typing: suppress a false error in mercurial/revlogutils/docket.py on py2
`ord()` wants bytes or str on py3, so I'm guessing it got confused by passing a
single byte instead of a one byte string. But this seems to work on 2.7.18
anyway.
Differential Revision: https://phab.mercurial-scm.org/D10876
local test passed
addgroupcopy test passed
clone test passed
lowlevelcopy test passed
slicing test passed
issnapshot test passed
findsnapshot test passed