Update link for Fundamental AI overview

Author: vishwaparekh

_layouts/default.html

@@ -35,7 +35,7 @@
         <li class="nav-parent">
           <span>Fundamental AI</span>
           <ul>
-            <li><a href="{{ '/research/fundamental-ai/' | relative_url }}">Overview</a></li>
+            <li><a href="{{ '/fundamental-ai/' | relative_url }}">Overview</a></li>
             <li><a href="{{ '/research/ai-safety/' | relative_url }}">AI Safety</a></li>
             <li><a href="{{ '/research/human-ai-ecosystems/' | relative_url }}">Human–AI Ecosystems</a></li>
           </ul>