fix broken reference to formatDate in a CommonJS environment

app/assets/javascripts/users/calendar.js

@@ -33,7 +33,7 @@
         date.setDate(date.getDate() + i);
         var day = date.getDay();
-        var count = timestamps[dateFormat(date, 'yyyy-mm-dd')];
+        var count = timestamps[date.format('yyyy-mm-dd')];
         // Create a new group array if this is the first day of the week
         // or if is first object
@@ -122,7 +122,7 @@
           if (stamp.count > 0) {
             contribText = stamp.count + " contribution" + (stamp.count > 1 ? 's' : '');
           }
-          dateText = dateFormat(date, 'mmm d, yyyy');
+          dateText = date.format('mmm d, yyyy');
           return contribText + "<br />" + (gl.utils.getDayName(date)) + " " + dateText;
         };
       })(this)).attr('class', 'user-contrib-cell js-tooltip').attr('fill', (function(_this) {