line 713 formatting and line 1853 correction

added ` to app/helpers/article_helper.rb  for formatting consistency.

line 1853 corrected file reference to `app/helpers/articles_helper.rb` as article_params was in the article helper module rather than article controller in tutorial.
Merge pull request #740 from Agsiegert/patch-10

line 713 formatting and line 1853 correction