added ScalaFiddle (s) (#2220)

added ScalaFiddle (s)

free-programming-playgrounds.md

@@ -70,4 +70,9 @@
 
 * [SQLFiddle](http://sqlfiddle.com)
 
+### Scala
+
+* [ScalaFiddle.io](https://scalafiddle.io/)
+* [ScalaFiddle.net](scalafiddle.net)
+