[fix] formatting

searx/templates/preferences.html

                 <td>{{ shortcuts[search_engine.name] }}</td>
                 <td>{{ _(categ) }}</td>
                 <td class="engine_checkbox">
-                    <input type="checkbox" id="engine_{{ categ}}_{{ search_engine.name|replace(' ', '_') }}" name="engine_{{ search_engine.name }}"{% if search_engine.name in blocked_engines %} checked="checked"{% endif %} />
+                    <input type="checkbox" id="engine_{{ categ }}_{{ search_engine.name|replace(' ', '_') }}" name="engine_{{ search_engine.name }}"{% if search_engine.name in blocked_engines %} checked="checked"{% endif %} />
                     <label class="allow" for="engine_{{ categ }}_{{ search_engine.name|replace(' ', '_') }}">{{ _('Allow') }}</label>
                     <label class="deny" for="engine_{{ categ }}_{{ search_engine.name|replace(' ', '_') }}">{{ _('Block') }}</label>
                 </td>