Add issue reference to nolint annotation

Usually errorlint allows io.EOF comparison (based on a whitelist of
functions that can return bare io.EOF), thus there is no need for nolint
annotation.

In this very case, though, the need for nolint is caused by issue with
errorlint, which fails to see where err is coming from.

Refer to the issue so when it is fixed we can remove the annotation.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

notify_socket.go

@@ -215,7 +215,7 @@ func sdNotifyBarrier(client *net.UnixConn) error {
 		// Probably the other end doesn't support the sd_notify_barrier protocol.
 		logrus.Warn("Timeout after waiting 30s for barrier. Ignored.")
 		return nil
-	} else if err == io.EOF { //nolint:errorlint // comparison with io.EOF is legit.
+	} else if err == io.EOF { //nolint:errorlint // https://github.com/polyfloyd/go-errorlint/issues/49
 		return nil
 	} else {
 		return err