Base plugins missing when extends base config

[andrey-pavlenko]

I am extending snowpack.config.js which has plugins. The inherited config also contains plugins. Base plugins are missing on build.

This behavior appears at snowpack@2.17.1. snowpack@2.17.0 works as expected.

Reproduced at https://github.com/andrey-pavlenko/showpack-extends

[ThomOrlo]

@andrey-pavlenko fixed by #2006