Update jQuery to 3.5.1 (#2713)

* Update jQuery to 3.5.1

Closes #2712

* Build NodeJS

Run using `npm run build:js`

docs/_docs/17-javascript.md

@@ -20,7 +20,7 @@ minimal mistakes
 |  |  |   └── smooth-scroll.js               # make same-page links scroll smoothly
 |  |  ├── vendor
 |  |  |   └── jquery
-|  |  |       └── jquery-3.4.1.js
+|  |  |       └── jquery-3.5.1.js
 |  |  ├── _main.js                           # jQuery plugin settings and other scripts
 |  |  └── main.min.js                        # concatenated and minified theme script
 ```