Fix typos and syntax errors in encode_test.go
Fix typos and syntax errors in encode_test.go

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