[Docs] Update node.js version in docs to v18 (#2558)

* Update DEVELOPERS.md, specify v18 Node.js required

Signed-off-by: Don McCurdy <donmccurdy@cartodb.com>

contributing/DEVELOPERS.md

@@ -22,7 +22,7 @@ machine:
 
 * [Git](http://git-scm.com/): The [Github Guide to Installing Git][git-setup] is a good source of information.
 
-* [Node.js ^14.x](http://nodejs.org): We use Node to generate the documentation, run a
+* [Node.js ^18.x](http://nodejs.org): We use Node to generate the documentation, run a
   development web server, run tests, and generate distributable files. Depending on your system,
   you can install Node either from source or as a pre-packaged bundle.