Fix the Elixir minimum version on guide to 1.5 (#3229)
Fix the Elixir minimum version on guide to 1.5 (#3229)

Starting from version 1.4, Phoenix generates the Elixir child spec
(making Elixir 1.5 the minimum working version for newly created
Phoenix 1.4 apps).
nshafer/phoenix,dmarkow/phoenix,michalmuskala/phoenix,eksperimental/phoenix,dmarkow/phoenix,jwarwick/phoenix,keathley/phoenix,eksperimental/phoenix,optikfluffel/phoenix,Joe-noh/phoenix,Gazler/phoenix,michalmuskala/phoenix,0x00evil/phoenix,nshafer/phoenix,optikfluffel/phoenix,Gazler/phoenix,jwarwick/phoenix,phoenixframework/phoenix,phoenixframework/phoenix,rafbgarcia/phoenix,0x00evil/phoenix,evax/phoenix,rafbgarcia/phoenix,Joe-noh/phoenix,optikfluffel/phoenix,phoenixframework/phoenix,evax/phoenix,mitchellhenke/phoenix,nshafer/phoenix,mitchellhenke/phoenix,keathley/phoenix,rafbgarcia/phoenix,0x00evil/phoenix