Update relative time text for a change updated to say "just now"

Previously, formatted dates would say "a few seconds ago" if the
timestamp was less than a minute in the past.  This change updates the
text to say "just now" instead.

Bug: Issue 4423
Change-Id: Ie8e4070ce3c1c57fc23bb3de4c110423a563ff19

polygerrit-ui/app/elements/shared/gr-date-formatter/gr-date-formatter.js

@@ -111,7 +111,12 @@
       var date = moment(util.parseDate(dateStr));
       if (!date.isValid()) { return ''; }
       if (relative) {
-        return date.fromNow();
+        var dateFromNow = date.fromNow();
+        if (dateFromNow === 'a few seconds ago') {
+          return 'just now';
+        } else {
+          return dateFromNow;
+        }
       }
       var now = new Date();
       var format = TimeFormats.MONTH_DAY_YEAR;