Bump simple-statistics from 7.8.3 to 7.8.4 #2319

Job	Run time
Helpers integration test (10.x)	1m 17s
Helpers integration test (12.x)	1m 28s
Helpers integration test (14.x)	1m 19s
Helpers integration test with secure cluster (10.x)	1m 11s
Helpers integration test (16.x)	1m 43s
Helpers integration test with secure cluster (12.x)	1m 20s
Helpers integration test (18.x)	1m 20s
Helpers integration test with secure cluster (14.x)	4m 27s
Helpers integration test with secure cluster (16.x)	2m 6s
Helpers integration test with secure cluster (18.x)	1m 5s
	17m 16s

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