Add backlink to verify mastodon (#978)

Gemfile

@@ -10,7 +10,7 @@ group :jekyll_plugins do
     gem 'jekyll-paginate-v2'
     gem 'jekyll-scholar'
     gem 'jekyll-sitemap'
-    gem 'jekyll-target-blank'
+    gem 'jekyll-link-attributes'
     gem 'jekyll-twitter-plugin'
     gem 'jemoji'
     gem 'mini_racer'

_config.yml

@@ -70,8 +70,7 @@ og_image: # The site-wide (default for all links) Open Graph preview image
 github_username: # your GitHub user name
 gitlab_username: # your GitLab user name
 twitter_username: # your Twitter handle
-mastodon_username: # your mastodon username
-mastodon_instance: # your mastodon instance
+mastodon_username: # your mastodon instance+username in the format instance.tld/@username
 linkedin_username: # your LinkedIn user name
 scholar_userid: # your Google Scholar ID
 semanticscholar_id: # your Semantic Scholar ID
@@ -190,7 +189,7 @@ plugins:
   - jekyll-paginate-v2
   - jekyll/scholar
   - jekyll-sitemap
-  - jekyll-target-blank
+  - jekyll-link-attributes
   - jekyll-twitter-plugin
   - jemoji
 
@@ -264,6 +263,18 @@ max_author_limit: 3  # leave blank to always show all authors
 more_authors_animation_delay: 10  # more authors are revealed on click using animation; smaller delay means faster animation
 
 
+# -----------------------------------------------------------------------------
+# Jekyll Link Attributes 
+# -----------------------------------------------------------------------------
+
+# These are the defaults
+external_links:
+  enabled: true
+  rel: external nofollow noopener
+  target: _blank
+  exclude:
+
+
 # -----------------------------------------------------------------------------
 # Responsive WebP Images
 # -----------------------------------------------------------------------------

_includes/social.html

@@ -28,8 +28,8 @@
             {%- if site.twitter_username -%}
             <a href="https://twitter.com/{{ site.twitter_username }}" title="Twitter"><i class="fab fa-twitter"></i></a>
             {% endif %}
-            {%- if site.mastodon_instance and site.mastodon_username -%}
-            <a rel="me" href="https://{{ site.mastodon_instance  }}/@{{site.mastodon_username}}" title="Mastodon"><i class="fab fa-mastodon"></i></a>
+            {%- if site.mastodon_username -%}
+            <a rel="me" href="https://{{ site.mastodon_username  }}" title="Mastodon"><i class="fab fa-mastodon"></i></a>
             {% endif %}
             {%- if site.medium_username -%}
             <a href="https://medium.com/@{{ site.medium_username }}" title="Medium"><i class="fab fa-medium"></i></a>