Require correct PHP version on composer

[ricardofiorani]

Since omnipay/common requires PHP 5 and this package doesn't require any PHP version BUT works only with PHP 7.1+, then it should have the right PHP version to be required in order to avoid this package being required in the wrong php environment.

[judgej]

The tests work down to PHP 5.6, so it certainly is compatible with PHP 5.6 at least. I'm going to try to keep compatibility with 5.6 while Omnipay Common does, probably another 6-9 months.

Is it the documentation that says 7.1?

[ricardofiorani]

@judgej on the readme it says:

This version only supports PHP 7.1+.

EDIT: @judgej I'll update it to match omnipay/common 's composer requirements and the documentation as well then.

[judgej]

Okay, it's probably the readme that is wrong. It did only support 7.1 at one point, but the 7.1+ syntax was so little used, that was changed.

[jamieburchell]

@judgej This change causes a composer "downgrade" to version 3.2.0 from >3.2.0 on PHP 8.0.