Framework: Bump recommended Node version to active LTS

Author: aduth

.nvmrc

@@ -1 +1 @@
-v6.11.1
+lts/*

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 ## Getting Started
 
-Gutenberg is a Node.js-based project, built primarily in JavaScript. Be sure to have <a href="https://nodejs.org/en/">Node.js installed first</a>. If you already have Node.js installed, make sure it's version 6.11.1 or higher for this plugin to work correctly. You can check your Node.js version by typing `node -v` in the Terminal prompt.
+Gutenberg is a Node.js-based project, built primarily in JavaScript. Be sure to have <a href="https://nodejs.org/en/">Node.js installed first</a>. You should be running a Node version matching the [current active LTS release](https://github.com/nodejs/Release#release-schedule) or newer for this plugin to work correctly. You can check your Node.js version by typing `node -v` in the Terminal prompt.
 
 You should also have the latest release of <a href="https://npmjs.org">npm installed</a>, npm is a separate project from Node.js and is updated frequently. If you've just installed Node.js which includes a version of npm within the installation you most likely will need to also update your npm install. To update npm, type this into your terminal: `npm install npm@latest -g`