Cast cross_val_score as a numpy.array

[Goto15]

In order to allow the use of mean(), cast the cross_val_score return data structure as a numpy.array. Also changed the in code comments to reflect the new return data structure.

Fixes #155

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[leouieda]

Thanks for submitting @Goto15! Just need a quick fix for the test and everything else should work. Good job!

[leouieda]

Suggested change

	>>> print('{:.2f}'.format(scores), sep = ", ")
	>>> print(', '.join(['{:.2f}'.format(score) for score in scores]))

We can keep the same test and it should work.

[Goto15]

I reverted the requested code, but might have accidentally committed the change twice. My bad.

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[leouieda]

No problem, we've all done this at some point 🙂

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