MQTT Library changed

[driverblock]

As of v 0.16.0, the Adafruit MQTT library no longer supports PROGMEM. As a result, the two examples will crash on ESP8266.

Please remove the lines referencing PROGMEM, and change the mqtt constructor to this:
// Setup the MQTT client class by passing in the WiFi client and MQTT server and login details. Adafruit_MQTT_Client mqtt(&client, AIO_SERVER, AIO_SERVERPORT, AIO_USERNAME, AIO_KEY);