Bump addressable from 2.7.0 to 2.8.0 in /docs (#374)

docs/Gemfile.lock

@@ -7,7 +7,7 @@ GEM
       minitest (~> 5.1)
       tzinfo (~> 1.1)
       zeitwerk (~> 2.2, >= 2.2.2)
-    addressable (2.7.0)
+    addressable (2.8.0)
       public_suffix (>= 2.0.2, < 5.0)
     coffee-script (2.4.1)
       coffee-script-source
@@ -219,6 +219,8 @@ GEM
       racc (~> 1.4)
     nokogiri (1.11.3-x86_64-darwin)
       racc (~> 1.4)
+    nokogiri (1.11.3-x86_64-linux)
+      racc (~> 1.4)
     octokit (4.20.0)
       faraday (>= 0.9)
       sawyer (~> 0.8.0, >= 0.5.3)
@@ -261,6 +263,7 @@ GEM
 
 PLATFORMS
   universal-darwin-20
+  x86_64-linux
 
 DEPENDENCIES
   github-pages (~> 214)