function _getPathFromNpm () {
  return new Promise((resolve) => {
    exec('npm config --global get prefix', (err, stdout) => {
      if (err) {
        resolve(null)
      } else {
        const npmPath = stdout.replace(/\n/, '')
        debug(`PowerShell: _getPathFromNpm() resolving with: ${npmPath}`)
        resolve(npmPath)
      }
    })
  })
}
Attempts to get npm's path by calling out to "npm config"

@returns {Promise.<string>} - Promise that resolves with the found path (or null if not found)