Fix calculation

Datasheet says: “The ADC converts an analog input voltage to a 10-bit
digital value through successive approximation. The minimum value
represents GND and the maximum value represents the voltage on the AREF
pin minus 1 LSB.”

Vcc.cpp

@@ -58,7 +58,7 @@ float Vcc::Read_Volts(void)
   // Result is now stored in ADC.
 
   // Calculate Vcc (in V)
-  float vcc = 1.1*1023.0 / ADC;
+  float vcc = 1.1*1024.0 / ADC;
 
   // Apply compensation
   vcc *= m_correction;