Date#parse requires a space between the seconds part and the timezone

The current logic results in `dateString` being set to e.g. `2005-02-15 00:00:00UTC` for DATETIME fields if UTC is set as the timezone. This results in an invalid date when passed to the `Date` constructor, or `NaN` when passed to `Date.parse` (the operation is the same internally for both methods).

With the fix, the date is parsed correctly.