Learn Ruby (#4310)

* Learn Ruby

Added a Ruby online material for learning

* Formatting updated

I formatted the contribution by fixing the alphabetical order of my Learn Ruby tutorial.

free-courses-en.md

@@ -472,6 +472,7 @@
 ### Ruby
 
 * [Learn how to program: Ruby](https://www.learnhowtoprogram.com/ruby) - Epicodus Inc.
+* [Learn Ruby](https://www.learnrubyonline.org)
 * [Ruby Tutorial](https://www.w3resource.com/ruby/)
 * [RubyMonk - Interactive Ruby tutorials](https://rubymonk.com)