Docstring: point to correct equivalent function

np.compress' "See also" pointed to itself instead to equivalent np.extract
Repaired my misunderstanding and added np.extract

I overlooked that np.compress and ndarray.compress are different things and wrongly assumed that it was a typo. I corrected that and added np.extract for equivalency for 1-D arrays.
Merge pull request #3538 from michaelaye/patch-1

Docstring: point to correct equivalent function (one word change)