fix spelling

main/sdr.go

@@ -50,7 +50,7 @@ func (e *ES) read() {
 	err := cmd.Start()
 	if err != nil {
 		log.Printf("Error executing /usr/bin/dump1090: %s\n", err
-		// don't return immediately, use the proper shutdown propcedure
+		// don't return immediately, use the proper shutdown procedure
 		shutdownES = true
 		for {
 			select {