Update README.md #281

Job	Run time
tests (3.2, 7.2)	5m 54s
tests (3.1, 7.1)	5m 26s
tests (3.2, 8.0)	5m 39s
tests (3.2, 7.1)	5m 23s
tests (3.1, 7.2)	5m 46s
tests (3.3, 8.0)	6m 17s
tests (3.3, 7.1)	5m 4s
tests (3.3, 7.2)	5m 49s
tests (3.3, edge)	26s
tests (head, 8.0)	18s
tests (3.4, 7.2)	6m 13s
tests (head, 7.1)	21s
tests (3.2, edge)	24s
tests (3.4, edge)	23s
tests (3.4, 8.0)	6m 5s
tests (head, edge)	25s
tests (3.3, 7.1, --enable-frozen-string-literal)	5m 36s
tests (head, 7.2)	18s
tests (3.4, 7.1)	5m 10s
	1h 10m 57s

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