BUGFIX: Fixed driveTime for real Roomba

- real roomba seems to need a longer drive time than the calculation
  dictates, so I added code that adds a multiplication by 1.3
  to driveTime_ if the roomba is not RoombaVirtual
BUGFIX: made the driveTime_ correction more accurate

- driveTime_ is now corrected by 1.25 instead of 1.3
ACCURACY_FIX: Changed DISTANCECORRECTION to a more accurate value

- DISTANCECORRECTION was changed to 8.133. It can still probably be
  made more accurate but this was needed.
- The driveTime_ was also adjusted according to this new fix
- further investigation to this real Roomba behavior would be
  beneficial.