Update Node to LTS

According to DF documentation, "Device Farm supports all Appium server versions 1.6.5 and above." Appium 1.21 & 1.22 requires at least Node v12, but the current Node version in DF is set to v10. How do I update the version or set it to a specific version? I tried "n lts" in the yaml file, but got "mkdir: cannot create directory ‘/usr/local/n’: Permission denied".

There are fixes in 1.21/1.22 that we need for mobile testing.