Error with duplicate package found in 2 separate `node_modules`

[yachaka]

Hi,

First, thanks for the package.
I'm having an error with a duplicate package, which is what I wanted, but the problem is that the duplicates are found inside node_modules, so I do not have the possibility to modify it.

It would be great to have an option to throw an error only when one of the duplicate is found in one of my own files.

[darrenscerri]

Hi @yachaka . Once #13 is merged this would be possible by excluding duplicates by issuer