emonTx_continuous_watthours sketch - error in the maths

An error has been found in the maths in the emonTx V2 version of this sketch. The effect of the error was to inflate the accumulated Watt.hours energy readings by exactly 25%, when the emonTx is calibrated to give the correct instantaneous power readings.

Github has been updated to reflect the changes, which are detailed here.

(The emonTx V3 version had minor updates done at the same time. The Github comment suggests that the error was in this version too, but that is not the case.)