Set flag which fixes build with v2.1.4 of WebSockets library

platformio.ini

@@ -30,6 +30,7 @@ test_ignore = remote
 upload_speed = 460800
 build_flags =
   !python .get_version.py
+  -D USING_AXTLS
   -D MQTT_MAX_PACKET_SIZE=250
   -D HTTP_UPLOAD_BUFLEN=128
   -D FIRMWARE_NAME=milight-hub