Bump rayon from 1.7.0 to 1.8.0 #145

Job	Run time
miri	2m 35s
build (ubuntu, stable, locked, true)	1h 5m 23s
build (windows, stable, locked, false)	1h 5m 50s
build (macos, stable, locked, false)	29m 23s
build (ubuntu, nightly, locked, false)	37m 19s
build (ubuntu, beta, locked, false)	35m 0s
build (ubuntu, stable, latest, false)	38m 56s
build (ubuntu, stable, minimal, false)	38m 22s
fuzz	17m 19s
deploy	0s
	5h 30m 7s

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