Update directory_structure.md (#4030)
Update directory_structure.md (#4030)

Fix a typo
phoenixframework/phoenix,0x00evil/phoenix,rafbgarcia/phoenix,nshafer/phoenix,optikfluffel/phoenix,optikfluffel/phoenix,0x00evil/phoenix,eksperimental/phoenix,phoenixframework/phoenix,0x00evil/phoenix,rafbgarcia/phoenix,eksperimental/phoenix,nshafer/phoenix,rafbgarcia/phoenix,nshafer/phoenix,phoenixframework/phoenix,optikfluffel/phoenix