heroku.md: Setup -> set up (#3850)
heroku.md: Setup -> set up (#3850)

"setup" is the noun and "set up" is the (phrasal) verb.
rafbgarcia/phoenix,rafbgarcia/phoenix,nshafer/phoenix,michalmuskala/phoenix,jwarwick/phoenix,optikfluffel/phoenix,jwarwick/phoenix,phoenixframework/phoenix,phoenixframework/phoenix,eksperimental/phoenix,nshafer/phoenix,michalmuskala/phoenix,phoenixframework/phoenix,0x00evil/phoenix,0x00evil/phoenix,0x00evil/phoenix,optikfluffel/phoenix,eksperimental/phoenix,rafbgarcia/phoenix,nshafer/phoenix,optikfluffel/phoenix