Add x86_64-linux platform to Gemfile.lock

Per rubygems/rubygems#4269

Author: timwis

Gemfile.lock

@@ -219,6 +219,8 @@ GEM
       racc (~> 1.4)
     nokogiri (1.13.9-x64-mingw32)
       racc (~> 1.4)
+    nokogiri (1.13.9-x86_64-linux)
+      racc (~> 1.4)
     octokit (4.25.1)
       faraday (>= 1, < 3)
       sawyer (~> 0.9)
@@ -261,6 +263,7 @@ GEM
 PLATFORMS
   ruby
   x64-mingw32
+  x86_64-linux
 
 DEPENDENCIES
   github-pages