Update generator_utils.py

[TanguyUrvoy]

Hi,
isinstance(v[0], six.integer_types) is False for np.int64 type causing algorithmic_sort_problem data generation to fail.

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[TanguyUrvoy]

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[afrozenator]

Thanks @TanguyUrvoy for this very important fix! I'll change the above to "np.issubdtype(type(v[0]), np.integer)" since it will generalize better. Thanks!

[afrozenator]

Many thanks @TanguyUrvoy !