Fix a bug that allowed unbounded upvotes.

If a user rated a venue at -3 ("Hate It"), that vote was not being
recorded. The update filter required a value between -2 and 3;
when I added the -3 rating button I failed to adjust this test.
Therefore, subsequent vote "changes" would bump up the venue's total
without changing the user's recorded vote -- thus allowing him/her to
continually increase the venue's score.
Merge branch 'fix-neg3-bug'