Description:
------------
The following signature

DateTimeZone::getOffset(DateTime $dateTime);

Should be:

DateTimeZone::getOffset(DateTimeInterface $dateTime);

Test script:
---------------
$tz = new DateTimeZone('Europe/London');
$dt = new DateTimeImmutable('2014-09-20', $tz);

echo $tz->getOffset($dt);

Expected result:
----------------
3600

Actual result:
--------------
PHP Warning:  DateTimeZone::getOffset() expects parameter 1 to be DateTime, object given in /Users/evert/code/foo.php on line 6