Allow using of psr/http-message v2.0

[spotman]

Hello, @snapshotpl!

Would you mind to allow using of psr/http-message:v2.0?
It can be done by updating dependencies in composer.json file:

require: {
  "psr/http-message": "^1.0 || ^2.0",
}

Thanks in advance!

Cheers,
Denis