Fix link to post path on categories#show

Bug introduced in #11.
¿ET TU?

POST_PATH(POST)

WHY WHY WHY WHY WHY WHY WHY

JUST PASS POST! DO NOT LET ME CATCH YOU DOING THIS AGAIN


![](http://img1.wikia.nocookie.net/__cb20130908173029/count-to-60/images/1/14/Son_i_am_disappoint.gif)