BF: Fixed example doctest in ndarray_offset

The integer data type changes between 32 and 64 bit operating
systems. Therefore, offset needed the correct itemsize.
Merge pull request #156 from Garyfallidis/ndarray_offset_doctest_fix

BF+MRG: Fixed example doctest in ndarray_offset

The integer data type changes between 32 and 64 bit operating
systems. Therefore, offset needed the correct itemsize.