added react-router to cheatsheets (#11774)

* added react-router to cheatsheets

* fixed linter

* Update more/free-programming-cheatsheets.md

Co-authored-by: Eric Hellman <eric@hellman.net>

---------

Co-authored-by: Eric Hellman <eric@hellman.net>

Author: uncleejay

more/free-programming-cheatsheets.md

@@ -307,6 +307,7 @@
 #### React.js
 
 * [React Cheatsheet](https://www.codecademy.com/learn/react-101/modules/react-101-jsx-u/cheatsheet) - Codecademy (HTML)
+* [React-router Cheatsheet](https://devhints.io/react-router) - Devhints.io (HTML)
 * [React.js Cheatsheet](https://devhints.io/react) - Devhints.io (HTML)
 * [Ultimate React.js Cheat Sheet](https://upmostly.com/ultimate-reactjs-cheat-sheet) - Upmostly.com (HTML)