composer installer 2.x support

[8ctopus]

$ composer require -W classicpress-plugins/classicpress-seo:^2.3.0
./composer.json has been updated
Running composer update classicpress-plugins/classicpress-seo --with-all-dependencies
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Root composer.json requires classicpress-plugins/classicpress-seo ^2.3.0 -> satisfiable by classicpress-
plugins/classicpress-seo[v2.3.0].
    - classicpress-plugins/classicpress-seo v2.3.0 requires composer/installers ~1.0 -> found composer/install
ers[v1.0.0, ..., 1.x-dev] but it conflicts with your root composer.json require (^2.2).

Bedrock now uses composer/installer:2.x

https://github.com/roots/bedrock/blob/efd54eff059ed8cfb6a897daa68499528c570134/composer.json#L35