Fix typing for Builder.placeholder

[justinchuby]

This pull request corrects the type of the shape parameter in Builder.placeholder.

[TobyRoseman]

Tuple seems like the better choice here to me. Why do you think it should be a Sequence?

[justinchuby]

From

coremltools/coremltools/converters/mil/mil/program.py

Lines 336 to 337 in 0434e85

	if not isinstance(sym_shape, (list, tuple, _np.ndarray)):
	raise ValueError("Illegal shape for Placeholder: {}".format(sym_shape))

it looks like shape needs to be list, tuple, _np.ndarray. Maybe setting to a union of these is appropriate then?

If we stick to tuples, it needs to be Tuple[Any, ...] to correctly accept a shape. Currently it only accepts 1-element tuples.

[TobyRoseman]

I agree it should be Tuple[Any, ...] not Tuple[Any]. I probably wouldn't worry about adding a Union.

[justinchuby]

Done