Update utterances-comment.html

_includes/utterances-comment.html

@@ -1,7 +1,7 @@
 {% if site.utterances.repository and site.utterances.issue-term  %}
 
 <script src="https://utteranc.es/client.js"
-        repository="{{site.utterances.repository }}"
+        repo="{{ site.utterances.repository }}"
         issue-term="{{ site.utterances.issue-term }}"
         theme="{{ site.utterances.theme}}"
         label="{{ site.utterances.label}}"