#17 Weekly activity bar graph lacks commits due to year change

[Anonymous]

In my private repository there are 8 commits made on 2012-12-31 and all of those increment non-existing week:
self.activity_by_year_week --> '2012-53': 8,

According to my calendar those commits should go to week 2013-01. I noticed this when I implemented my own "Recent activity" bar graph showing amount of daily commits. My numbers on week 01 didn't match with numbers in Weekly activity bar graph.