cmd/go: indent first test binary flag description for `go test -h`

Fixes #12642

Change-Id: I0b94437055b7d444f5caf7ea310e85357c467bdf
Reviewed-on: https://go-review.googlesource.com/14612Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/main.go

@@ -286,7 +286,7 @@ func usage() {
 	// special case "go test -h"
 	if len(os.Args) > 1 && os.Args[1] == "test" {
 		os.Stdout.WriteString(testUsage + "\n\n" +
-			strings.TrimSpace(testFlag1) + "\n\n" +
+			strings.TrimSpace(testFlag1) + "\n\n\t" +
 			strings.TrimSpace(testFlag2) + "\n")
 		os.Exit(2)
 	}