Update solution.md

1-js/05-data-types/03-string/2-check-spam/solution.md

@@ -1,6 +1,6 @@
 To make the search case-insensitive, let's bring the string to lower case and then search:
 
-```js run
+```js run demo
 function checkSpam(str) {
   let lowerStr = str.toLowerCase();