fix: support npm5’s --save default for postinstall script

[janl]

We now check PWD for node_modules, i.e.: we are only
in node_modules if we are doing npm install hoodie
somewhere, but not when running npm install in the
hoodie source directory.

Closes #746

[janl]

Ping @hoodiehq/maintainers <3

[gr2m]

I can’t get hoodie to install with npm5, it fails with an Cannot read property 'find' of undefined error. I think the problem is isaacs/node-glob#341

$ node -v && npm -v && npm i hoodie
v8.0.0
5.0.2
npm WARN deprecated minimatch@2.0.10: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm ERR! Cannot read property 'find' of undefined
npm ERR! Cannot read property 'find' of undefined

Does it work for you?

[janl]

Works fine with:

v6.9.1
5.0.2

[gr2m]

I get the same error

$ npm init -y
Wrote to /private/tmp/hoodie-issues-760/package.json:

{
  "name": "hoodie-issues-760",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}


$ npm i hoodie
npm WARN deprecated minimatch@2.0.10: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm ERR! Cannot read property 'find' of undefined
npm ERR! Cannot read property 'find' of undefined

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/gregor/.npm/_logs/2017-06-03T17_52_05_262Z-debug.log
$ node -v
v6.9.5
$ npm -v
5.0.2

This is very weird...

[gr2m]

okay my problem was unrelated and could be fixed via npm/npm#16677 (comment).

Checking the PR now