Update free-programming-playgrounds.md (#2754)

* Update free-programming-playgrounds.md

* remove trailing slash

free-programming-playgrounds.md

@@ -1,6 +1,7 @@
 ### Index
 
 * [Angular](#angular)
+* [ClojureScript](#clojurescript)
 * [Crystal](#crystal)
 * [CSS](#css)
 * [FlexBox](#flexbox)
@@ -24,6 +25,11 @@
 * [Plunker](http://plnkr.co)
 
 
+### ClojureScript
+
+* [Web REPL](http://clojurescript.net)
+
+
 ### Crystal
 
 * [Compile & run code in Crystal](https://play.crystal-lang.org/#/cr)