Fix dependencies installation

[Lctrs]

I suspect that the dependencies has been updated with a higher PHP version than 7.2.0, our minimal supported PHP version.

[Ocramius]

LGTM, although we should start bumping to ^7.4 for the package itself (it's stable now, can be one safely)

[kukulich]

Is it useful for us to bump PHP to ^7.4 ? I can do it and add types to properties but I already know that @ondrejmirtes will have to revert all my changes in his fork to support even PHP 7.1.

[Ocramius]

Well, over here, development needs to proceed, and we'll need to start working on 8.x support as next feature. PHP 7.2~7.3 support will be dropped much before those go EOL: if support for older versions if needed, it will be in older minor releases

[kukulich]

So can we release 4.0.0 with ^7.2 and bump PHP to ^7.4 then?

[Ocramius]

Seems acceptable

[ondrejmirtes]

I've wanted to write a tool that would convert 7.4 code to 7.1 anyway :D So I can write PHPStan in phpstan-src in PHP 7.4 only, but still support PHP 7.1 in the PHAR.

[Ocramius]

If you are working on that, see https://github.com/endel/galapagos