disqus: fixed issue #199 (#200)

CONTRIBUTORS.md

@@ -40,3 +40,4 @@
 - [Łukasz Mróz](https://github.com/mrozlukasz)
 - [Jia "Jay" Tan](https://github.com/j7an)
 - [Ryan](https://github.com/alrayyes)
+- [Naim A.](https://github.com/naim94a)

layouts/partials/posts/disqus.html

@@ -1,3 +1,3 @@
-{{- if and (isset .Site "disqusshortname") (not (eq .Site.DisqusShortname "" )) (eq (.Params.disable_comments | default false) false) -}}
+{{- if and (not (eq (.Site.DisqusShortname | default "") "")) (eq (.Params.disable_comments | default false) false) -}}
   {{ template "_internal/disqus.html" . }}
 {{- end -}}