Allow use of PSR-7 v2

[Crell]

PSR-7 v2 just adds types, which should be safe in virtually any circumstances. It does require PHP 7.2 or higher, but allowing either version should allow Composer to figure it out.

Without this, having React installed makes a project incompatible with any package that depends on PSR-7 v2, which is a non-small number.

(I haven't tried running this locally yet; I am assuming CI will indicate if there's an issue.)

[Crell]

... A segfault? I am confused.

[WyriHaximus]

... A segfault? I am confused.

It's a bit of a long story: friends-of-reactphp/mysql#205

[WyriHaximus]

Just merged #543 that will resolve the segfault

[Crell]

Oh, that thing...

[Crell]

Hm, it's still locking psr/http-message 1.1, even on newer PHP versions that would support 2.0. I'm not sure why.

[Bilge]

composer why-not psr/http-message ^2

[Crell]

ringcentral/psr7 1.3.0 requires psr/http-message (~1.0) 

Well [expletive deleted]. That package appears to be abandoned. I don't know if switching to nyholm/psr7 (which is supported and solid) is viable, but this sounds like a larger problem.

[kwhat]

@Crell I've added the required changes for psr/http-message ^2.0 to PR #542, however, I solved the ringcentral/psr7 problem by removing clue/http-proxy-react from the dependencies as it is only used in 1 example. Have you tried contacting clue/http-proxy-react to see if they would be open to moving to nyholm/psr7 or similar? It would be nice if we could keep the example.