message: test for yarn in a folder that will not have a package.json
diff: 'use strict'
  const _ = require('lodash')
  +const os = require('os')
  const path = require('path')
  const semver = require('semver')
  const Bluebird = require('bluebird')
  @@ -243,7 +244,7 @@ class PackageManager {
  let paths = this.getBasePaths()
  let yarnDir = null
  // check if homebridge was installed using yarn
  - return childProcess.execAsync('yarn global dir')
  + return childProcess.execAsync('yarn global dir', {cwd: os.tmpdir()})
  .then(data => {
  yarnDir = path.join(data.trim(data), 'node_modules')
  paths.push(yarnDir)
  