[runtime] Upgrade Node.js to version 16

Node.js 16.x just landed on Vercel! 🎈
https://vercel.com/changelog/node-js-16-lts-is-now-available

...only a few hours after the runtime actually landed on AWS itself: 👌
aws/aws-lambda-base-images#14 (comment)

Author: Olivier Philippon

.nvmrc

@@ -1 +1 @@
-14
+16

README.md

@@ -6,10 +6,10 @@ We welcome PRs to add projects to the Rich / Textual galleries. Can't promise we
 
 ## Start dev server for maintaining purpose
 
-You will need Node.js (version 14, as newer versions are not supported by our hosting platform at the moment) to run the site locally.  
+You will need Node.js (version 16 to run the site locally.  
 Using [nvm](https://github.com/nvm-sh/nvm#intro) is the recommended way to install such a version. Once it is installed, you can run the following commands:
 
--   `nvm install 14 && nvm use 14` - installs Node.js v14
+-   `nvm install 16 && nvm use 16` - installs Node.js v14
 -   `npm i` - installs the Node.js dependencies
 -   `npm run dev` - starts the local development server
 

package-lock.json

@@ -2,7 +2,7 @@
     "private": true,
     "name": "Textualize.io",
     "engines": {
-        "node": "14.x"
+        "node": "16.x"
     },
     "scripts": {
         "dev": "next dev",