Typo in Evaluation.md

[Ivo Schaper]

There is a typo in the Evaluation.md regarding how the metric tests can be invoked:
run-timeline-metric-tests -t /path/to/timelines

whereas it should be:
run-timeline-metrics-tests -t /path/to/timelines

Hope this will save anyone at least a little bit of time.

[Sebastian Martschat]

Thank you for spotting the error! Fixed in 7cd812f.