Enforce matching engines on npm install

[sholladay]

Fixes #480

This PR enables the engine-strict configuration for npm install when np reinstalls the dependencies. This will raise an error if the project or its dependencies have an engines.node in package.json that are incompatible with the current environment.

A question: should this be applied to the npm ci case as well? I ran npm ci --engine-strict in a package whose engines.node was incompatible with the current Node version and it did not complain, whereas npm install --engine-strict did complain in the same situation. However, I did not test what happens when dependencies have mismatched engines. I also did not test using the npm config environment variable, only the command line flag. Perhaps an implementation quirk leads to npm ci loading configuration differently.

[sindresorhus]

should this be applied to the npm ci case as well?

Yes. While there's no difference now, the problem might be fixed at some point, so it doesn't hurt to include it.

Perhaps an implementation quirk leads to npm ci loading configuration differently.

I wouldn't be surprised if this was the case. npm has a lot of weird quirks.

[sholladay]

All review feedback has been addressed. :)

[itaisteinherz]

LGTM

[itaisteinherz]

Thanks @sholladay! 🙂