Adicionar kotlin (EbookFoundation#2607)

Author: thyagoluciano

free-programming-playgrounds.md

@@ -7,6 +7,7 @@
 * [Go](#go)
 * [Haskell](#haskell)
 * [JavaScript](#javascript)
+* [Kotlin](#kotlin)
 * [.Net](#dotnet)
 * [Node.js](#nodejs)
 * [Perl](#perl)
@@ -61,6 +62,11 @@
 * [WebpackBin](https://www.webpackbin.com)
 
 
+### Kotlin
+
+* [Kotlin](https://try.kotlinlang.org)
+
+
 ### <a name="dotnet"></a>.NET
 
 * [.NET Fiddle](https://dotnetfiddle.net)