make conference footer only available when there are conferences to display

Author: inescoelho

_data/conferences.yml

@@ -20,5 +20,7 @@ <h4>{{ package.name }}</h4>
   </li>
 {% endfor %}
 <p>Note: the stars on the logos represent the number of RGSoC editions supported by the sponsor</p>
-{% include conferences_footer.html %}
+{% if site.data.conferences %}
+  {% include conferences_footer.html %}
+{% endif %}
 </ul>