goleak at the util/sem:sem_test

[hawkingrei]

Bug Report

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1. Minimal reproduce step (Required)

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3. What did you see instead (Required)

goleak: Errors on successful test run: found unexpected goroutines:
[Goroutine 16 in state select, with go.opencensus.io/stats/view.(*worker).start on top of the stack:
goroutine 16 [select]:
go.opencensus.io/stats/view.(*worker).start(0xc000379200)
	external/io_opencensus_go/stats/view/worker.go:292 +0x9f
created by go.opencensus.io/stats/view.init.0 in goroutine 1
	external/io_opencensus_go/stats/view/worker.go:34 +0x8d
]
-- 

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