Add support for npm workspaces

[targos]

See example in https://github.com/targos/nsecure-workspace

Result of nsecure cwd is included in the repo.

Modules structure:

node-secure data:

We see that only the top-level lodash dependency was analyzed.

[targos]

Note that the package-lock does contain information about all the dependencies.

[fraxken]

PR opened here: #25

[fraxken]

Available in v3.3.0.