__get_dtype fails when type is list

[beasteers]

This is relevant for scaper's schema e.g.:

    "pitch_shift": {
      "type": ["number", "null"]
    },

It should be handled similar to oneOf:

def __get_dtype(typespec):
    '''Get the dtype associated with a jsonschema type definition
    Parameters
    ----------
    typespec : dict
        The schema definition
    Returns
    -------
    dtype : numpy.dtype
        The associated dtype
    '''

    if 'type' in typespec:
        if isinstance(typespec['type'], (list, tuple)):
            # get dtype for each type in list
            types = [__TYPE_MAP__.get(t, np.object_) for t in typespec['type']]

            # If they're not all equal, return object
            if all([t == types[0] for t in types]):
                return types[0]
            return np.object_
        else:
            return __TYPE_MAP__.get(typespec['type'], np.object_)

    elif 'enum' in typespec:
        # Enums map to objects
        return np.object_

    elif 'oneOf' in typespec:
        # Recurse
        types = [__get_dtype(v) for v in typespec['oneOf']]

        # If they're not all equal, return object
        if all([t == types[0] for t in types]):
            return types[0]

    return np.object_