Fix broken ReplayWeb.page form

We removed a (seemingly superfluous) class name in a previous commit,
which broke the form because the JS was expecting to find an element
with that class name.

layouts/shortcodes/replayweb-url.html

@@ -1,5 +1,5 @@
 {{- .Page.Scratch.Set "replayweb" true -}}
-<div class="card my-4">
+<div class="replayweb-url-form card my-4">
   <div class="card-body">
     <form novalidate>
       <div class="row align-itesm-center mb-2 needs-validated slug-input">