Update itertools requirement from 0.13 to 0.14 #2326

Job	Run time
maybe-expedite	3s
lint	3m 34s
test (third-party, bincode, stable, false)	12m 16s
test (third-party, bincode, stable, true)	11m 28s
test (third-party, bincode, nightly, false)	10m 35s
test (third-party, bincode, nightly, true)	11m 17s
test (third-party, postcard, stable, false)	12m 38s
test (third-party, postcard, stable, true)	12m 0s
test (third-party, postcard, nightly, false)	11m 13s
test (third-party, postcard, nightly, true)	10m 54s
test (other, bincode, stable, false)	24m 32s
test (other, bincode, stable, true)	25m 26s
test (other, bincode, nightly, false)	30m 1s
test (other, bincode, nightly, true)	30m 38s
test (other, postcard, stable, false)	26m 45s
test (other, postcard, stable, true)	26m 11s
test (other, postcard, nightly, false)	32m 52s
test (other, postcard, nightly, true)	32m 23s
all-checks	1s
	5h 24m 47s

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