title: Convert \DateTimeImmutable to \DateTime
body: <p>How can I convert a <a href="http://php.net/manual/class.datetimeimmutable.php" rel="noreferrer"><code>DateTimeImmutable</code></a> object into a <a href="http://php.net/manual/class.datetime.php" rel="noreferrer"><code>DateTime</code></a> object?</p>