doc: Use w.Write instead of fmt in yaml_docs

benchmark                        old ns/op     new ns/op     delta
BenchmarkGenYamlToFile-4         62488         61622         -1.39%

benchmark                        old allocs     new allocs     delta
BenchmarkGenYamlToFile-4         121            120            -0.83%

benchmark                        old bytes     new bytes     delta
BenchmarkGenYamlToFile-4         26706         26280         -1.60%

doc/yaml_docs.go

@@ -130,7 +130,8 @@ func GenYamlCustom(cmd *cobra.Command, w io.Writer, linkHandler func(string) str
 		fmt.Println(err)
 		os.Exit(1)
 	}
-	if _, err := fmt.Fprintf(w, string(final)); err != nil {
+
+	if _, err := w.Write(final); err != nil {
 		return err
 	}
 	return nil

doc/yaml_docs_test.go

@@ -106,3 +106,20 @@ func TestGenYamlTree(t *testing.T) {
 		t.Fatalf("Expected file 'do.yaml' to exist")
 	}
 }
+
+func BenchmarkGenYamlToFile(b *testing.B) {
+	c := initializeWithRootCmd()
+	file, err := ioutil.TempFile("", "")
+	if err != nil {
+		b.Fatal(err)
+	}
+	defer os.Remove(file.Name())
+	defer file.Close()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		if err := GenYaml(c, file); err != nil {
+			b.Fatal(err)
+		}
+	}
+}