Use aliased attribute methods in EventCalendar

In 'adjust_all_day_dates', use the aliased attribute methods 'start_at'
and 'end_at' rather than 'self[:start_at]' and 'self[:end_at]' just in
case someone's using all-day events with custom models using attributes
other than 'start_at' and/or 'end_at'.

lib/event_calendar.rb

@@ -175,12 +175,13 @@ def clip_range(start_d, end_d)
     end
 
     def adjust_all_day_dates
-      if self[:all_day]
-        self[:start_at] = self[:start_at].beginning_of_day
-        if self[:end_at]
-          self[:end_at] = self[:end_at].beginning_of_day + 1.day - 1.second
+      if self.all_day
+        self.start_at = self.start_at.beginning_of_day
+
+        if self.end_at
+          self.end_at = self.end_at.beginning_of_day + 1.day - 1.second
         else
-          self[:end_at] = self[:start_at].beginning_of_day + 1.day - 1.second
+          self.end_at = self.start_at + 1.day - 1.second
         end
       end
     end