replace simple regex with a native Ruby method (#6732)

Merge pull request 6732

lib/jekyll/reader.rb

@@ -78,7 +78,7 @@ module Jekyll
       dot_dirs.each do |file|
         dir_path = site.in_source_dir(dir, file)
         rel_path = File.join(dir, file)
-        unless @site.dest.sub(%r!/$!, "") == dir_path
+        unless @site.dest.chomp("/") == dir_path
           @site.reader.read_directories(rel_path)
         end
       end