Supporting PSR-17 and PSR-18

[Florian Voutzinos]

This Exchanger PR florianv/exchanger#71 added support for both PSR-17 and PSR-18.

We need to allow both in Swap as well:

• https://github.com/florianv/swap/blob/master/src/Builder.php#L18-L19
• https://github.com/florianv/swap/blob/master/src/Service/Factory.php#L56-L57