Made fixes specific to ESP devices only

Author: ShVerni

src/DFRobot_EnvironmentalSensor.h

@@ -16,6 +16,9 @@
 #include "Arduino.h"
 #include "Wire.h"
 #include "DFRobot_RTU.h"
+#if !defined(ESP8266) && !defined(ESP32)
+#include "String.h"
+#endif
 
 #if (defined ARDUINO_AVR_UNO) && (defined ESP8266)
 #include "SoftwareSerial.h"