Add Lua, MATLAB, and Ruby courses, check_urls=free-courses-en.md (#5065)

* Add Lua, MATLAB, and Ruby courses, check_urls=free-courses-en.md

* Fix alphabetical ordering of Lua course

free-courses-en.md

@@ -436,6 +436,7 @@
 
 ### Lua
 
+* [Learn Lua in 15 Minutes](http://tylerneylon.com/a/learn-lua/) - Tyler Neylon (HTML)
 * [Lua Interactive Crash Course](http://luatut.com/crash_course.html)
 * [Lua Tutorial](http://www.tutorialspoint.com/lua/)
 
@@ -462,6 +463,7 @@
 ### MATLAB
 
 * [Data Processing and Feature Engineering with MATLAB](https://www.coursera.org/learn/feature-engineering-matlab) (coursera)
+* [MATLAB and Simulink Training](https://matlabacademy.mathworks.com)
 * [MIT 18.S997 Introduction to MATLAB Programming](http://ocw.mit.edu/courses/mathematics/18-s997-introduction-to-matlab-programming-fall-2011/)
 
 
@@ -592,6 +594,7 @@
 
 ### Ruby
 
+* [An Introduction to Ruby Programming Language](https://www.researchgate.net/publication/322222154_An_Introduction_to_Ruby_Programming_Language) - Ali Tourani (HTML, PDF)
 * [Learn how to program: Ruby](https://www.learnhowtoprogram.com/ruby) - Epicodus Inc.
 * [Learn Ruby](https://www.learnrubyonline.org)
 * [RESTful API with Ruby On Rails 5](https://www.udemy.com/course/restful-api-with-ruby-on-rails-5/) - Udemy