Refactor fizzBuzz function in README_EN.md

Refactor fizzBuzz function to use switch-case and improve performance.

Author: yanglbme

solution/0400-0499/0412.Fizz Buzz/README_EN.md

@@ -129,21 +129,21 @@ public:
 #### Go
 
 ```go
-func fizzBuzz(n int) (ans []string) {
-	for i := 1; i <= n; i++ {
-		s := &strings.Builder{}
-		if i%3 == 0 {
-			s.WriteString("Fizz")
+func fizzBuzz(n int) []string {
+	ans := make([]string, 0, n)
+	for i := 1; i < n+1; i++ {
+		switch {
+		case i%15 == 0:
+			ans = append(ans, "FizzBuzz")
+		case i%3 == 0:
+			ans = append(ans, "Fizz")
+		case i%5 == 0:
+			ans = append(ans, "Buzz")
+		default:
+			ans = append(ans, strconv.Itoa(i))
 		}
-		if i%5 == 0 {
-			s.WriteString("Buzz")
-		}
-		if s.Len() == 0 {
-			s.WriteString(strconv.Itoa(i))
-		}
-		ans = append(ans, s.String())
 	}
-	return
+	return ans
 }
 ```