docs: do not specify upper copyright year (#30)

Author: keradus

theme/layout.html

@@ -86,7 +86,7 @@ <h1 class="title_header">
     {%- block footer %}
       <footer class="ft">
         <div class="content">
-          The <a href="{{ pathto('_static/images/logo.png', 1) }}">logo</a> is &copy; 2010-2023 Sensio Labs
+          The <a href="{{ pathto('_static/images/logo.png', 1) }}">logo</a> is &copy; 2010+ Sensio Labs
         </div>
       </footer>
     {%- endblock %}