Use a consistent spelling of acknowledgments

There were a lot of uses of acknowledg**e**ments in this class, which I think is the wrong spelling. (Or at least a less common spelling.)

It was definitely conflicting with https://github.com/DangerCove/Acknowledge which generates `Acknowledgments.rtf` (No "E") but this code was looking for a `Acknowledgements.rtf` (With an "E").