Allow ^1.0 || ^2.0 in psr/container

[Ayesh]

FIG released a new version of psr/container today. The new 2.x series has parameter types and return types, but it does not remove any methods.

Technically, we are compatible with any psr/container ^1.0 || ^2.0 implementation. This PR updates the required psr/container versions to include 2.x as well, so users can use any psr/container implementation, including ones that implement the new version.

I use my own container implementation with phpwatch/simple-container, that just tagged 2.0.0 with psr/container ^2.0 requirement. I think other containers will follow suit in coming weeks.

Thank you.

[coveralls]

Coverage remained the same at 100.0% when pulling 6c71e5d on Ayesh:psr-container2 into bdc423b on slimphp:4.x.

[l0gicgate]

We should do this on all the other repos as well. Thank you for your contribution @Ayesh