Fix js2coffee-replace-region when mark is after point

When the mark is after the point, calling js2coffee-replace-region doesn't give the desired output and generally results with the original js code with a few characters deleted.

This is because call-process-region inserts the output in the buffer before the point, and then delete-region ends up deleting the resulting coffee code.

call-process-region already has an option of providing a fourth non-nil argument to delete the text between start and end.