Declare dependency on guzzlehttp/psr7

[wouterj]

This package uses functions from guzzlehttp/psr7, which are removed in psr7 2.0. As no dependency was declared, it was possible to install psr7 2.0 together with this package, resulting in fatal errors. By declaring the dependency, we can limit psr7 to 1.x.

After #469 is merged, the version constraint can be updated to ^1.7 || ^2.0 (as the static method API used in that PR was introduced in 1.7.0).

[GrahamCampbell]

Guzzle maintainer here. You should instead upgrade to replacement functions. They are available on 1.x and 2.x.

[wouterj]

@GrahamCampbell yes, both actions should be done (declare dependency if you depend on something the package provides & use the BC layer for 2.0). That's what I meant with (#469 is doing the method replacement):

After #469 is merged, the version constraint can be updated to ^1.7 || ^2.0 (as the static method API used in that PR was introduced in 1.7.0).

Seems like this was forgotten, I've submitted a new PR to fix the constraint: #480