Update Rakefile

Co-authored-by: Olle Jonsson <olle.jonsson@gmail.com>

Author: st0012

Rakefile

@@ -22,7 +22,7 @@ task :default => :test
 task rdoc: :generate
 RDoc::Task.new do |doc|
   # RDoc task defaults to /html and overrides the op_dir option in .rdoc_options
-  doc.rdoc_dir = "_site"
+  doc.rdoc_dir = "_site" # for github pages
 end
 
 task "coverage" do