Travis Ci - Use a specific Node version on a PHP container

For a Laravel project I use Travis Ci with the language option as PHP. Besides PHP I want to do some Node JS testing. The default installed version of Node JS does not meet my requirements. How can I specify the version of Node JS in my config file?

I have tried the following. But unfortunately, that does not work.

language: php

php:
  - '7.0'
  - '7.1'

node_js:
  - '6.10'

via maartenpaauw