upgrade to Sabredav 1.5.4

3rdparty/Sabre.includes.php

3rdparty/Sabre/CardDAV/AddressBook.php

3rdparty/Sabre/CardDAV/Backend/Abstract.php

3rdparty/Sabre/CardDAV/Backend/PDO.php

3rdparty/Sabre/CardDAV/Card.php

3rdparty/Sabre/CardDAV/ICard.php

3rdparty/Sabre/CardDAV/Plugin.php

3rdparty/Sabre/CardDAV/UserAddressBooks.php

3rdparty/Sabre/CardDAV/Version.php

3rdparty/Sabre/DAV/Browser/GuessContentType.php

3rdparty/Sabre/DAV/Server.php

3rdparty/Sabre/DAV/Version.php

3rdparty/Sabre/DAVACL/Exception/NeedPrivileges.php

3rdparty/Sabre/DAVACL/PrincipalCollection.php

3rdparty/Sabre/VObject/Component.php

3rdparty/Sabre/VObject/Element/DateTime.php

3rdparty/Sabre/VObject/Element/MultiDateTime.php

3rdparty/Sabre/VObject/Node.php

3rdparty/Sabre/VObject/Property.php

3rdparty/Sabre/VObject/Reader.php