`topk` in the `options` for `imageClassifier` doesn't work

[jackbdu]

In [email protected], when initializing the imageClassifier object, passing { topk: 5 } as options does not seem to affect the number of labels to return. On the other hand, specifying kNumber works fine when calling imageClassifier.classifyStart(media, ?kNumber, callback);

Tagging relevant issues/PRs for reference: #71 #83