Update WiFi_MQTT_Adafruit.io.ino

Update example to new HTS221 APIs

Author: cparata

examples/Boards/STM32L475VG-DISCOVERY-IOT/WiFi_MQTT_Adafruit.io/WiFi_MQTT_Adafruit.io.ino

@@ -80,6 +80,7 @@ void setup() {
 
   // Initlialize components.
   HumTemp = new HTS221Sensor (dev_i2c);
+  HumTemp->begin();
   HumTemp->Enable();
 }