fixed the apostrophe on "isn't".

Author: CrazyKitty357

404.md

@@ -10,4 +10,4 @@ title: "404"
   </a>
   <figcaption>404 image by <a href="https://x.com/sawaratsuki1004">@sawaratsuki1004</a></figcaption>
 </figure>
-Error 404! This page isn't found! head back to [blog home]({{ site.baseurl }}/)
+Error 404! This page isn't found! head back to [blog home]({{ site.baseurl }}/)