node requirement

[ajhsu]

After failed twice when doing npm install with node@4.7.3, I found that package needs node >= 6.4 to build up.
So I think that it would be great to indicate specific node version that package required ( node >= 6.4 ) in README file.

[seantcanavan]

package.json lists:

  "engines": {
    "node": ">=8.2"
  },