Signal server done before closing connections

This fixes the races we are seeing in the tests

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

.travis.yml

@@ -1,6 +1,6 @@
 language: go
 
 go:
-  - 1.9.x
+  - "1.10.x"
 
 script: go test -race -v ./...

server.go

@@ -127,13 +127,13 @@ func (s *Server) Serve(ctx context.Context, l net.Listener) error {
 
 func (s *Server) Shutdown(ctx context.Context) error {
 	s.mu.Lock()
-	lnerr := s.closeListeners()
 	select {
 	case <-s.done:
 	default:
 		// protected by mutex
 		close(s.done)
 	}
+	lnerr := s.closeListeners()
 	s.mu.Unlock()
 
 	ticker := time.NewTicker(200 * time.Millisecond)