add default constructor in place of constructor() method

Adafruit_Sensor.cpp

@@ -1,5 +1,2 @@
 #include "Adafruit_Sensor.h"
 #include <avr/pgmspace.h>
-
-void Adafruit_Sensor::constructor() {
-}

Adafruit_Sensor.h

@@ -139,7 +139,7 @@ typedef struct
 class Adafruit_Sensor {
  public:
   // Constructor(s)
-  void constructor();
+  Adafruit_Sensor() {}
   virtual ~Adafruit_Sensor() {}
 
   // These must be defined by the subclass