[handler-broker] Fix typo in core interfaces
[handler-broker] Fix typo in core interfaces

TheThingsNetwork/ttn,jvanmalder/ttn,LoRaWanSoFa/ttn,TheThingsNetwork/ttn,LoRaWanSoFa/ttn,jvanmalder/ttn,mgranberry/ttn,jvanmalder/ttn,mgranberry/ttn,TheThingsNetwork/ttn,mgranberry/ttn