Flow Sensor calculation

[Shoban94]

https://github.com/DexterInd/GrovePi/blob/master/Firmware/Source/v1.2/grove_pi_v1_2_6/grove_pi_v1_2_6.ino#L751

Looks like the factor should be 7.5 and not 73

[DexterInd]

@karan259 do you want to weigh in on this?

[karan259]

@DexterInd this is just a small conversion factor error that Shoban found when answering a question on the forum and we are going to update it in the firmware and just added a note here so that we dont forget it