Fixes admin session cookie test

- Currently the test is taking the response date
which is in UTC and passes it through moment()
which by default parses input as local time.  We
then add 12 hours to this now local time
and when compared against the response set-cookie
header the time spread is wrong.

- To fix we’re parsing the response date with
moment.utc which parses the date in UTC.

core/test/functional/routes/admin_test.js

@@ -64,7 +64,7 @@ describe('Admin Routing', function () {
 
                     var expires;
                     // Session should expire 12 hours after the time in the date header
-                    expires = moment(res.headers.date).add('Hours', 12).format("ddd, DD MMM YYYY HH:mm");
+                    expires = moment.utc(res.headers.date).add('Hours', 12).format("ddd, DD MMM YYYY HH:mm");
                     expires = new RegExp("Expires=" + expires);
 
                     res.headers['set-cookie'].should.match(expires);