Inconsistent return types for start() and conversion24bit()

[Srijal97]

The return type for HX711_ADC::start() is int, though it does not return anything.
The return type for HX711_ADC::conversion24bit() is uint8_t, though it also returns nothing.

It does compile fins with these errors in Arduino IDE, but I am getting errors in Sloeber. I have fixed them by modifying the source code, I suggest this is done here as well.

[olkal]

Thanks, corrected in 1.2.4