fix: don't fail if critters is missing on Next.js>=10.0.4

[erezrokah]

- Summary

Related to netlify/next-on-netlify#103 (comment)
Doesn't fix the original issue as the original issue is about a missing react-native module (we don't have a reproduction for it).

This is a result of a recent change in Next.js

Note: This use case is not covered by the logic that makes

zip-it-and-ship-it/tests/main.js

Line 127 in 1e248c6

await zipNode(t, 'node-module-deep-conditional')

pass, since we tree shake Next.js dependencies instead of copying published files, side files and nested modules.

A better solution would be to support configuring external modules (see #68) so the Next.js plugin (or any other plugin) can generate a relevant bundling configuration based on the framework.
That bundling configuration can change based on the site configuration, for example if the user has optimizeCss configured for their Next.js site, we would like to bundle the critter dependency.

Regardless, this is an issue with Next.js as critters should be an optional dependency.

- Test plan

Added unit tests

- Description for the changelog

Don't fail when critters module is missing on Next.js>=10.0.4

- A picture of a cute animal (not mandatory but encouraged)

[ehmicky]

Should we abstract this by taking the module names and versions from some constant variable such as:

const EXTERNAL_MODULES = {
  critters: { next: '>= 10.0.4' }
}

This would allow adding more of those.

Alternatively we could also wait for another case of external module to abstract, but then maybe we should rename isExternalModule() to isExternalCrittersModule()?

[erezrokah]

Alternatively we could also wait for another case of external module to abstract

Let's wait for another use case.
Not sure we want this to be a long term fix anyway.