Fixed typo in contexts.md (#4459)
Fixed typo in contexts.md (#4459)


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