updated the generate_sdk_methods.py script to fix the pre_attachment[*] params

updated the generate_sdk_methods.py script to fix the pre_attachment[*] params defined in the canvas rest api. this param definition is incorrect, it's merely a placeholder for params defined on this page: https://canvas.instructure.com/doc/api/file.file_uploads.html. They are content_type, parent_folder_id, parent_folder_path, folder, and on_duplicate. the update detects the pre_attachment param and substitutes in the correct parameters.