fix to prevent us trapped in calibration mode forever

platformio.ini

@@ -12,7 +12,7 @@
 platform = espressif32
 board = esp32dev
 framework = arduino
-upload_port = COM5
+upload_port = /dev/ttyUSB0
 lib_deps = 
 	adafruit/Adafruit NeoPixel@^1.6.0
 	wifwaf/MH-Z19@^1.5.2

src/ebk_co2ampel.cpp

@@ -83,6 +83,7 @@ void setup() {
     display.clear();
     display.drawString(64, 0, "DONE");
     display.display();
+    preferences.putUInt("cal", 42);
     char myVersion[4];          
     myMHZ19.getVersion(myVersion);
     Serial.print("\nFirmware Version: ");