fix(footer): Define itemtype property

The properties copyrightYear and copyrightHolder refer to the nearest parent CreativeWork.
https://schema.org/CreativeWork

Partially fixes: #401

Signed-off-by: Khusika Dhamar Gusti <mail@khusika.com>

layouts/partials/footer.html

@@ -17,7 +17,7 @@
                 </div>
             {{- end -}}
 
-            <div class="footer-line">
+            <div class="footer-line" itemscope itemtype="http://schema.org/CreativeWork">
                 {{- /* Copyright year */ -}}
                 {{- if ne .Site.Params.footer.copyright false -}}
                     <i class="far fa-copyright fa-fw"></i>