comments.html: Shorten if condition (#44)

Signed-off-by: Stephan Kulla <git.mail@kulla.me>

layouts/partials/comments.html

@@ -1,4 +1,4 @@
-{{ if and (and (not (eq .Site.DisqusShortname "")) (not (isset .Site.Params "disable_comments")) (not (isset .Params "disable_comments"))) }}
+{{ if and .Site.DisqusShortname (not (or .Site.Params.disable_comments .Params.disable_comments)) }}
 <section id="comments">
   <div id="disqus_thread">
     {{ template "_internal/disqus.html" . }}