fix mastodon verification

themes/hugo-sustain/layouts/partials/social.html

@@ -5,7 +5,7 @@
     {{ end }}
 
     {{- with .Site.Params.Social.Mastodon -}}
-      <li><a href="https://{{- . -}}" title="Mastodon"><i class="fab fa-mastodon"></i></a></li>
+      <li><a href="https://{{- . -}}" title="Mastodon" rel="me"><i class="fab fa-mastodon"></i></a></li>
     {{ end }}
 
     {{- with .Site.Params.Social.Twitter -}}