[graceful] Specs are failing randomly

[EtienneM]

Specs of the graceful package are failing randomly:

--- FAIL: TestService_Restart (0.01s)

    service_test.go:104: 

        	Error Trace:	service_test.go:104

        	Error:      	Received unexpected error:

        	            	Get "http://localhost:9000/?sleep=20": read tcp 127.0.0.1:46390->127.0.0.1:9000: read: connection reset by peer

        	Test:       	TestService_Restart

FAIL

FAIL	github.com/Scalingo/go-utils/graceful	2.499s

For instance: https://travis-ci.com/github/Scalingo/go-utils/builds/188846288