3883 Include works from December 31 in stats totals for the year

https://code.google.com/p/otwarchive/issues/detail?id=3883

```
start_date = DateTime.parse("01/01/#{@current_year}")
end_date = DateTime.parse("31/12/#{@current_year}")
work_query = work_query.where("works.revised_at >= ? AND works.revised_at <= ?", start_date, end_date)
```

Basically, it wasn't getting the works from 31/12 when it was tallying kudos or what have you. Changing it to `01/01/#{next_year}` where `next_year = current_year.to_i + 1` does the trick because 31/12 is included in the range.