perf!: rename comment setting parameter (cotes2020#1563)

Rename `site.comments.active` to `site.comments.provider`

_config.yml

@@ -98,8 +98,9 @@ social_preview_image: # string, local or CORS resources
 toc: true
 
 comments:
-  active: # The global switch for posts comments, e.g., 'disqus'.  Keep it empty means disable
-  # The active options are as follows:
+  # Global switch for the post comment system. Keeping it empty means disabled.
+  provider: # [disqus | utterances | giscus]
+  # The provider options are as follows:
   disqus:
     shortname: # fill with the Disqus shortname. › https://help.disqus.com/en/articles/1717111-what-s-a-shortname
   # utterances settings › https://utteranc.es/