[fix] update path resolution to npm

[kwonoj]

Hi, I liked this module and would like to utilize this in some of my codebases, sending PR to enhance couple of behavior.

• resolve root path via app-root-path, provides platform compatible path
  : Usually for Windows user who runs different shells will have issues by determining root via git can returns shell-specific path like \c\apps\myapp.... instead, introduced app-root-path (https://github.com/inxilpro/node-app-root-path) to resolve root path to application.
• fixes npm-which invocation to correctly resolves npm
  one thing I noticed is this module calls npm-which with name of linter as npmWhich(linter,...) which causes npm-which fails all time since npm-which expects file to lookup (npm, in this case). Updated to lookup npm, leave fallback to default binPath as-is.

[okonet]

Thanks for the PR! I didn't know about app-root-path. Nice!

Regarding the npmWhich change: with this change it won't work without having all tasks set explicitly in scripts section. I think for most users this is an overkill. See also #17. I'm writing tests now that will cover all the edge cases.

Would you mind splitting the PR to 2. I would merge the app-root one right now.

[kwonoj]

I think for most users this is an overkill. See also #17. I'm writing tests now that will cover all the edge cases.

: that makes sense. Let me separate PR and dig npm-which bit more. It'd be great to have coverage to ensure no regressions.

[kwonoj]

I've amended this PR for including app-root-path only as suggested.

[okonet]

Awesome! I'll review and merge soon.