ideal_labeler: label() should return the label instead of list

[lsc36]

Current IdealLabeler seems to return a list of labels instead of the label.

self.y[np.where([...])[0]]

should be

self.y[np.where([...])[0]][0]

or

self.y[np.where([...])[0][0]]

[lsc36]

Clarified: label() accepts multiple features and should return a list.