Update Rakefile

Co-authored-by: Benjamin Quorning <[email protected]>

Rakefile

@@ -77,7 +77,7 @@ task confirm_documentation: :generate_cops_documentation do
 
   unless status.success?
     puts 'Documentation is out of sync:'
-    puts stdin
+    puts stdout
     raise 'Please run `rake generate_cops_documentation` ' \
           'and add docs/ to the commit.'
   end