templates: login: Use /login/ as endpoint
Needed because otherwise the POST-ed data will be sent to a
redirect from /login to /login/, triggering an unnecessary
browser warning.
<main>
<div id="login">
Administration secured by password:
- <form method="POST" action="{{isso_host_script}}/login">
+ <form method="POST" action="{{isso_host_script}}/login/">
<input type="password" name="password" autofocus />
</form>
</div>
