Update CREDITS.md

CREDITS.md

@@ -1,5 +1,9 @@
 Credits
 =======
+  
+  - Showdown v2
+    * [Estevão Santos](https://github.com/tivie)
+
   - Showdown v1
     * [Estevão Santos](https://github.com/tivie)
     * [Pascal Deschênes](https://github.com/pdeschen)