Use PSR-17 factory from Guzzle/psr7 2.0

[t0mmy742]

http-interop/http-factory-guzzle recommends to use PSR-17 implementation from guzzlehttp/psr7 if we can use version ^2.0. Since it matches our dependencies, I replaced old package with the new one.
Users can still use http-interop/http-factory-guzzle if they add it manually.

Closes #3105

[coveralls]

Coverage remained the same at 100.0% when pulling 45607c9 on t0mmy742:support_guzzle_psr17_2_0 into c431514 on slimphp:4.x.

[l0gicgate]

This shouldn’t break any downstream projects since they would already have Guzzle PSR-7 which includes the Psr17 factories correct?

[t0mmy742]

@l0gicgate Since we dropped support for guzzlehttp/psr7:^1.0 and updated to ^2.0, people using this PSR-7 provider already have PSR-17 factory.
If keeping http-interop/http-factory-guzzle is something wanted, people already installed it manually since it's not in our requirement packages.
TODO: We should update README file to specify version of supported PSR-7 providers.

[ArrayIterator]

On version (current / 4.8.1 release) not yet update.

Slim/Slim/Factory/Psr17/GuzzlePsr17Factory.php

Line 15 in c8934c3

protected static $responseFactoryClass = 'Http\Factory\Guzzle\ResponseFactory';

Any info about released from current master?

[l0gicgate]

@ArrayIterator just release 4.9.0 which features the changes.