Bump up EOL version

Author: hsbt

Rakefile

@@ -56,7 +56,7 @@ URI_BASE = 'https://cache.ruby-lang.org/pub/ruby/'
 
 # 'rake sync' checks the tarballs in the directories after RUBY_EOL_VERSION.
 # https://www.ruby-lang.org/en/downloads/branches/
-RUBY_EOL_VERSION = '2.6'
+RUBY_EOL_VERSION = '3.1'
 
 def make_entry(relpath)
   uri = URI_BASE + relpath