Add link to 1.6 upgrade guide to changelog (#4503)
Add link to 1.6 upgrade guide to changelog (#4503)


phoenixframework/phoenix,rafbgarcia/phoenix,optikfluffel/phoenix,nshafer/phoenix,nshafer/phoenix,phoenixframework/phoenix,0x00evil/phoenix,nshafer/phoenix,0x00evil/phoenix,0x00evil/phoenix,rafbgarcia/phoenix,phoenixframework/phoenix,optikfluffel/phoenix,optikfluffel/phoenix,rafbgarcia/phoenix