Upgrade to latest arrow to include set serialization speedups

[pcmoritz]

see apache/arrow#1060

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[robertnishihara]

Though it technically doesn't change the behavior, we should probably also remove these lines, right?

ray/python/ray/worker.py

Lines 1031 to 1032 in d6612a9

	# Tell Ray to serialize sets with pickle.
	_register_class(type(set()), pickle=True)

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