Update svn1 node versions for Gutenberg

As per #4974-meta for future CoreCore Core is the set of software required to run WordPress. The Core Development Team builds WordPress. builds the NodeJS/NPM versions will need bumping for proper GutenbergGutenberg The Gutenberg project is the new Editor Interface for WordPress. The editor improves the process and experience of creating new content, making writing rich content much simpler. It uses ‘blocks’ to add richness rather than shortcodes, custom HTML etc. https://wordpress.org/gutenberg/ building. The PR won’t be merged prior to the svn build servers being updated.

Gutenberg now requires Node.js 12.x and npm > 6.9.x and the “build server” requires updating to accommodate this.
At the time of creating this ticket:
* the latest Node.js LTS release is 12.14.1 https://nodejs.org/en/
* the latest npm release is 6.13.6 https://blog.npmjs.org/
See also: https://github.com/WordPress/gutenberg/pull/19680

For any questions, you’ll need to follow up with someone more involved with Gutenberg development, see the above TracTrac Trac is the place where contributors create issues for bugs or feature requests much like GitHub.https://core.trac.wordpress.org/. ticket or Gutenberg PR.