Fixed broken tests

• results of linear interpolation in itk v5 have slightly changed Due to rounding effect (uchar pixel type) the become problematic. The results are still plausible so the reference images are updated.
• The nrrd output style has changed int itk5 thus simple file comparison with expandingFieldKernelWriterTest_ref.nrrd let to an error. Content (vector field) is still the same. Replaced the reference file.