Fix sphinx requirement to add overlap

When I63c6159eb23430a181eb20016b35366c2fbbf9f8 was implemented it
didn't include any overlap with the previous required versions,
which causes breakage in the gate while the change is being tested
and until the mirror updates. For completeness add the suggested
overlap back in for now.

Change-Id: I70559a2b6eb961bf1c5fbe8006cd1275c39577b6
Co-Authored-By: Doug Hellmann <doug.hellmann@dreamhost.com>
Merge "Fix sphinx requirement to add overlap"