[fix] form submit url

searx/templates/search.html

-<form method="post" action="" id="search_form">
+<form method="post" action="/" id="search_form">
 <div id="search_wrapper">
     <input type="text" class="q" name="q" tabindex="1" autocomplete="off" {% if q %}value="{{ q }}"{% endif %}/>
     <input type="submit" value="" id="search_submit" />