Remove Google+

Google+ is being shutdown on April 2, 2019. Social sharing buttong, comment provider, and author link configs have been removed from the theme.

ref: https://support.google.com/plus/answer/9195133

docs/_config.yml

@@ -24,7 +24,7 @@ masthead_title           : # overrides the website title displayed in the masthe
 # breadcrumbs            : false # true, false (default)
 words_per_minute         : 200
 comments:
-  provider               : "false" # false (default), "disqus", "discourse", "facebook", "google-plus", "staticman_v2", "staticman", "utterances", "custom"
+  provider               : "false" # false (default), "disqus", "discourse", "facebook", "staticman_v2", "staticman", "utterances", "custom"
   disqus:
     shortname            :
   discourse: