Fix voltage reference in examples

examples/Analog_input/Analog_input_0_10V/Analog_input_0_10V.ino

@@ -20,7 +20,7 @@
 using namespace machinecontrol;
 
 float res_divider = 0.28057;
-float reference = 3.3;
+float reference = 3.0;
 
 void setup() {
   analogReadResolution(16);

examples/Analog_input/Analog_input_4_20mA/Analog_input_4_20mA.ino

@@ -21,7 +21,7 @@ using namespace machinecontrol;
 
 #define SENSE_RES 120
 
-float reference = 3.3;
+float reference = 3.0;
 
 void setup() {
   analogReadResolution(16);

examples/Analog_input/Analog_input_NTC/Analog_input_NTC.ino

@@ -26,7 +26,7 @@ using namespace machinecontrol;
 
 #define REFERENCE_RES 100000
 
-float reference = 3.3;
+float reference = 3.0;
 float lowest_voltage = 2.7;
 
 void setup() {