Changed type of inner value.
Changed type of inner value.

The `result` value was a tuple, but the first element of that tuple was
never used, so it seems reasonable to remove it.

fscheck/FsCheck,ErikSchierboom/FsCheck,jhamm/FsCheck,fsharp/FsCheck,sideeffffect/FsCheck,ploeh/FsCheck,fscheck/FsCheck