Don't use python-Levenshtein 0.11.0

A fix is here https://github.com/ztane/python-Levenshtein/pull/1

0.11.0 add Python 3 support, so not something we really need right now.
So until the fix lands, and since it is so close to a final release, let
us be conservative and make sure we're only using the working version.