fix TestHttpProbe/returns_the_status_code_if_the_request_is_successful

[abdoroot]

Fixes #52.

[jesusprubio]

Thank you! I would prefer to merge a proper solution instead this workaround.

The problem here is the function newTestHTTPServer returning before the server is listening. Because the call to ListenAndServe is made inside a goroutine: https://github.com/jesusprubio/up/blob/520cd9e9fc0c35e2b1be6f70106bf6ed222bb54a/pkg/protocols_test.go#L66-L67

Please check this solution. I think it should work: https://stackoverflow.com/a/53332769

[abdoroot]

thanks for suggestion it work