Added Javascript30 Course from Wesbos (#4457)

* Update free-courses-en.md

Added Flexbox & CSS Grid free video resources to the repo

* Update free-courses-en.md

* Update free-courses-en.md

Removed the trailing slashes from the root domain

* Update free-courses-en.md

Added free Javascript30 course from Wesbos

free-courses-en.md

@@ -279,6 +279,7 @@
 * [Egghead.io](https://egghead.io)
 * [Intro to JavaScript ES6 programming](https://www.youtube.com/playlist?list=PL-xu4i_QDSxcoDNeh8rx5-pHCCTOg0XsI)
 * [Javascript Essentials](https://www.udemy.com/javascript-essentials/) - Lawrence Turton (Udemy)
+* [Javascript30](https://javascript30.com) - Wesbos
 * [Learn how to program: JavaScript](https://www.learnhowtoprogram.com/javascript) - Epicodus Inc.
 * [learn:query](https://learnquery.infinum.co)