Fix typo on Persistent chapter (thanks Erlend Hamberg)
Fix typo on Persistent chapter (thanks Erlend Hamberg)

wolftune/yesodweb.com-content,wolftune/yesodweb.com-content,maxigit/yesodweb.com-content,maxigit/yesodweb.com-content,mlitchard/lambdaweb.com-content