Typo correction

http://stackoverflow.com/questions/14097615/yesod-persistent-entity-deriving-show/14098490
Merge branch 'just-asciidoc' of /home/ubuntu/sites/yesodweb.com/content/book/tools/../..
Merge commit '2af9e53b1a9634a90db99290e44273a25fe7942b'