Fixed something wrong.

2.2.md

@@ -395,7 +395,7 @@ slice有一些简便的操作
 	// map有两个返回值，第二个返回值，如果不存在key，那么ok为false，如果存在ok为true
 	csharpRating, ok := rating["C#"]
 	if ok {
-		fmt.Println("C# is in the map and its rating is ", csharp_rating)
+		fmt.Println("C# is in the map and its rating is ", csharpRating)
 	} else {
 		fmt.Println("We have no rating associated with C# in the map")
 	}