Remove / in url_for parameter for simple theme

Same change as with the oscar theme.

searx/templates/simple/macros.html

@@ -9,7 +9,7 @@
 
 <!-- Draw favicon -->
 {% macro draw_favicon(favicon) -%}
-    <img width="14" height="14" class="favicon" src="{{ url_for('static', filename='/themes/simple/img/icons/' + favicon + '.png') }}" alt="{{ favicon }}" />
+    <img width="14" height="14" class="favicon" src="{{ url_for('static', filename='themes/simple/img/icons/' + favicon + '.png') }}" alt="{{ favicon }}" />
 {%- endmacro %}
 
 {% macro result_open_link(url, classes='') -%}