fix(strain report): Displays correct time units in plots

WHY IS THIS CHANGE NEEDED?:
- sampling_period parameter replaced by unit_scaling in swain-lab/aliby/postprocessor!15
- units off by 5

HOW DOES THE CHANGE SOLVE THE PROBLEM?:
- should be self-explanatory

WHAT SIDE EFFECTS DOES THIS CHANGE HAVE?:
- may break the fft plot's horizontal axis

EVIDENCE THAT COMMIT WORKS:
- checked the output pdf, numbers make sense, except the fft plot