fix: update footer

Author: mostafaei2002

Diff for: docs_theme/main.html

@@ -121,8 +121,8 @@
     </div>
     <!--/.wrapper -->
 
-    <footer class="span12">
-      <p>
+    <footer class="col-11 border-top mx-auto">
+      <p class="text-center py-3 my-0">
         Documentation built with <a href="http://www.mkdocs.org/">MkDocs</a>.
       </p>
     </footer>