Fix Rails version in Gemfile snippets

Fixed the Rails version in Gemfile snippets to match the ‘Getting
started on Mavericks’ guide.  Also removed the ‘~>’  in the second
Gemfile snippet.
Merge pull request #23 from nixw/gemfile_snippet_fix

Fix Rails version in Gemfile snippets
Updating middleman s3_sync
Merge branch 'master' into develop