Update blogger.markdown for attr_accessible in I4.

Updated I4 not to use attr_accessible for the :image attribute (as rails throws an error on using attr_accessible and advises using strong parameters) and update the articles_controller#article_params to permit :image instead (https://github.com/sudarshanshubakar/jsl_blogger/blob/master/app/controllers/articles_controller.rb).

BTW, this is my first pull request ever, so please feel free to guide me in case this isn't what you are expecting.