Fixed bug with getWeekId 

Theres an apparent bug in getWeekId (Dec 31, 2013 would give 'dh-2013-0' instead of...'dh-2014-0'). This appears to be because getDayForWeek might move to the next year (week 0 may include some dates from the previous year). The if (m === 11 && w === 1) { appeared to be a workaround, but doesnt work because week numbers start at 0. However just basing the id of getDayForWeek() seems to fix it and be simpler.