Add support for utterrances label (#384)

Arunvel Sriram

11.13.2020 ba1028a9d09059b3ea2fcbf53cb319bdb206da19

 layouts/partials/posts/utterances.html

@@ -3,6 +3,7 @@
  <script src="https://utteranc.es/client.js"
    repo= "{{ .Site.Params.utterances.repo }}"
    issue-term="{{ default "title" .Site.Params.utterances.issueTerm }}"
    {{ if isset .Site.Params.utterances "label" }}label="{{ .Site.Params.utterances.label }}"{{ end }}
    theme="{{ default "github-light" .Site.Params.utterances.theme }}"
    crossorigin="anonymous"
    async>