3.4.0.2 - Fix PHP 7.4 issues

Fix get_magic_quotes_gpc depreciation on PHP 7.4

Fix get_magic_quotes_gpc depreciation on PHP 7.4
when ipn messages are received.

magic quotes feature was removed in PHP 5.4.0
should not need to test for it on PHP 7 and above.

3.4.0.1 - PHP 7.4

Fix PHP 7.4 bug in PPXmlMessage

* ErrorException: Cannot use "parent" when current class scope has no parent
  vendor/paypal/sdk-core-php/lib/PayPal/Core/PPXmlMessage.php:124

  As class has no parent, changed to self instead.

* Update travis config with new php versions