tests: log value of IsTerminal

Just log the output of IsTerminal in TestTerminal.

$ go test -v -run TestTerminal
=== RUN   TestTerminal
    isatty_others_test.go:13: os.Stdout: true
--- PASS: TestTerminal (0.00s)
PASS
ok  	github.com/mattn/go-isatty	0.160s
$ go test -v -run TestTerminal | cat
=== RUN   TestTerminal
    isatty_others_test.go:13: os.Stdout: false
--- PASS: TestTerminal (0.00s)
PASS
ok  	github.com/mattn/go-isatty	0.203s

isatty_others_test.go

@@ -10,7 +10,7 @@ import (
 
 func TestTerminal(t *testing.T) {
 	// test for non-panic
-	IsTerminal(os.Stdout.Fd())
+	t.Log("os.Stdout:", IsTerminal(os.Stdout.Fd()))
 }
 
 func TestCygwinPipeName(t *testing.T) {