Reduce step size in test_rotspring.
Reduce step size in test_rotspring.

NOTES:
- with the previous step size h=5e-4, this test passes with the INT_ANITESCU timestepper.
- with the new default timestepper INT_EULER_IMPLICIT_LINEARIZED, discrepancies in the angular acceleration and reaction torque for Case 1 are now above the prescribed tolerance.
- the change in step size (now h = 2e-4) is a temporary solution.
- we should investigate the cause of the differences between the two timesteppers.

projectchrono/chrono-validation