Merge pull request #1471 from andyleiserson/update-tokio #5501

Job	Run time
Basic Checks	20m 18s
Measure coverage	27m 27s
Additional Builds and Concurrency Tests	15m 24s
miri	3m 6s
Release builds and tests	11m 44s
sanitize (address)	16m 17s
sanitize (address, multi-threading)	18m 43s
sanitize (leak)	8m 39s
Slow tests	14m 32s
sanitize (leak, multi-threading)	8m 8s
	2h 24m 18s

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