fix(playground): correct link to upstream playground

Author: amaanq

cli/src/playground.html

@@ -37,7 +37,7 @@
       </div>
 
       <div class=header-item>
-        <a href="https://tree-sitter.github.io/tree-sitter/playground#about">(?)</a>
+        <a href="https://tree-sitter.github.io/tree-sitter/7-playground.html#about">(?)</a>
       </div>
 
       <select id="language-select" style="display: none;">