Composer: allow composer installers 2.x

[jrfnl]

Context

• Users requiring this package via [WP]Packagist can now use the composer/installers v2.

Summary

This PR can be summarized in the following changelog entry:

• Users requiring this package via [WP]Packagist can now use the composer/installers v2.

Relevant technical choices:

While the latest version of the composer/installers package is 2.2, I'm explicitly setting the version constraint to a lenient one as this is a non-dev requirement, which comes into play when people use a [WP]Packagist based site setup.

If we set the requirement very strictly, it could conflict with other plugins with different constraints and it is not as if any of the 2.x releases have touched the WordPress installer, so setting it to || 2.0 should be fine.

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• N/A

[coveralls]

Pull Request Test Coverage Report for Build 6408268041

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 48.608%

---

Totals
Change from base Build 6408034137:	0.0%
Covered Lines:	1100
Relevant Lines:	2263

---

💛 - Coveralls