Fix typo in html tag (#10990)

* Updated 404.html

fixed the typo in hr tag.

* updated 404.html

I resolved the error in line 74 of public/404.html.

* Update 404.html

public/404.html

@@ -41,7 +41,7 @@ <h1>That page does not exist.</h1>
 
           <p>Are you sure you've typed the right address?</p>
 
-          <hr />
+          <hr>
 
           <p>Please help us figure out what happened so we can fix it!</p>