[fix] use proper encoding with both py2/3 - closes #1094

searx/templates/simple/404.html

 <div class="center">
     <h1>{{ _('Page not found') }}</h1>
     {% autoescape false %}
-    <p>{{ _('Go to %(search_page)s.', search_page='<a href="{}">{}</a>'.decode('utf-8').format(url_for('index'), _('search page'))) }}</p>
+    <p>{{ _('Go to %(search_page)s.', search_page=unicode('<a href="{}">{}</a>').format(url_for('index'), _('search page'))) }}</p>
     {% endautoescape %}
 </div>
 {% endblock %}