Use strict to solve syntax error on some devices

error_pages/404.html

@@ -253,6 +253,7 @@
 		</div>
 	</div>
 	<script>
+		"use strict";
 		window.onload = function() {
 			let wl = window.location.pathname;
 			let out = wl.replace(/&/g,'&amp;').replace(/</g,'&lt;').replace(/>/g,'&gt;');