Update list of mix tasks in tasks guide (#3095)
Update list of mix tasks in tasks guide (#3095)

* Remove hardcoded 1.3.0 reference

* Update Phoenix specific mix tasks section

rafbgarcia/phoenix,nshafer/phoenix,Kosmas/phoenix,eksperimental/phoenix,michalmuskala/phoenix,mitchellhenke/phoenix,nshafer/phoenix,mitchellhenke/phoenix,phoenixframework/phoenix,optikfluffel/phoenix,optikfluffel/phoenix,0x00evil/phoenix,rafbgarcia/phoenix,evax/phoenix,Kosmas/phoenix,michalmuskala/phoenix,jwarwick/phoenix,dmarkow/phoenix,Gazler/phoenix,evax/phoenix,nshafer/phoenix,optikfluffel/phoenix,phoenixframework/phoenix,phoenixframework/phoenix,keathley/phoenix,0x00evil/phoenix,rafbgarcia/phoenix,eksperimental/phoenix,Joe-noh/phoenix,Joe-noh/phoenix,keathley/phoenix,dmarkow/phoenix,jwarwick/phoenix,Gazler/phoenix,0x00evil/phoenix