vulndb/govulncheck: avoid printing redundant newlines

For golang/go#49350

Change-Id: I6d3c50f56a61e666235e6d2e0ba3231768575218
Reviewed-on: https://go-review.googlesource.com/c/exp/+/361854
Run-TryBot: Zvonimir Pavlinovic <zpavlinovic@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Zvonimir Pavlinovic <zpavlinovic@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>

vulndb/govulncheck/main.go

@@ -81,11 +81,11 @@ func init() {
 }
 
 func main() {
-	flag.Usage = func() { fmt.Fprintln(os.Stderr, usage) }
+	flag.Usage = func() { fmt.Fprint(os.Stderr, usage) }
 	flag.Parse()
 
 	if len(flag.Args()) == 0 {
-		fmt.Fprintln(os.Stderr, usage)
+		fmt.Fprint(os.Stderr, usage)
 		os.Exit(1)
 	}