doc: fix typo in The Laws of Reflection article

R=golang-dev, gri, r
CC=golang-dev
https://golang.org/cl/5876047
diff --git a/doc/progs/interface2.go b/doc/progs/interface2.go
index 2deba32..a541d94 100644
--- a/doc/progs/interface2.go
+++ b/doc/progs/interface2.go
@@ -123,3 +123,10 @@
 	fmt.Println("t is now", t)
 	// STOP OMIT
 }
+
+func f9() {
+	// START f9 OMIT
+	var x float64 = 3.4
+	fmt.Println("value:", reflect.ValueOf(x))
+	// STOP OMIT
+}