Adjust RMS error for displacement field for IRM3 test

Based on the difference errors reported on the dashboard the error has
been adjusted, the values are reasonable for a rms of a displacement
field for a affine transformation.

Change-Id: I78e20136e0a8a3e50e2a43dd7c7b91fd80e797bf
Merge topic 'SIMPLEITK-575_AddAccessorToOptimizerScales' into next

c5f0452b Adjust RMS error for displacement field for IRM3 test