Missing case in enum

[FStefanni]

Hi,

just to signal this warning:

ESP32_LoRaWAN/src/ESP32_LoRaWAN.cpp:422:12: error: enumeration value 'LORAMAC_REGION_LA915' not handled in switch [-Wswitch]

In my code I use -Werror=switch to transform the warning into an error, since missing enum cases in switches is usually a hidden bug. But then this lib does not compile... So it could be nice to handle the missing case in the switch.

If you like, I can also propose a pr.

Thank you, regards.