Include only whole days in Differential stats

Summary: This prevents "8 active days" for last week.

Test Plan: `strtotime('1 week ago 24:00')`

Reviewers: john, epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D2794

src/applications/differential/view/DifferentialRevisionStatsView.php

@@ -68,7 +68,7 @@ final class DifferentialRevisionStatsView extends AphrontView {
                '1 year', '18 months',
                '2 years', '3 years', '4 years', '5 years',
              ) as $age) {
-      $dates[$age] = strtotime($age . ' ago');
+      $dates[$age] = strtotime($age . ' ago 24:00');
       $counts[$age] = 0;
       $lines[$age] = 0;
       $count_active[$age] = 0;