ch7: fix code format

ch7/ch7-01.md

@@ -8,6 +8,7 @@
 
 ``` go
 package fmt
+
 func Fprintf(w io.Writer, format string, args ...interface{}) (int, error)
 func Printf(format string, args ...interface{}) (int, error) {
 	return Fprintf(os.Stdout, format, args...)
@@ -26,6 +27,7 @@ Fprintf的前綴F表示文件(File)也表明格式化輸出結果應該被寫入
 
 ``` go
 package io
+
 // Writer is the interface that wraps the basic Write method.
 type Writer interface {
 	// Write writes len(p) bytes from p to the underlying data stream.
@@ -45,21 +47,23 @@ io.Writer類型定義了函數Fprintf和這個函數調用者之間的約定。
 
 讓我們通過一個新的類型來進行校驗，下面\*ByteCounter類型里的Write方法，僅僅在丟失寫向它的字節前統計它們的長度。(在這個+=賦值語句中，讓len(p)的類型和\*c的類型匹配的轉換是必須的。)
 
+<u><i>gopl.io/ch7/bytecounter</i></u>
 ```go
-// gopl.io/ch7/bytecounter
 type ByteCounter int
+
 func (c *ByteCounter) Write(p []byte) (int, error) {
-    *c += ByteCounter(len(p)) // convert int to ByteCounter
-    return len(p), nil
+	*c += ByteCounter(len(p)) // convert int to ByteCounter
+	return len(p), nil
 }
 ```
+
 因爲*ByteCounter滿足io.Writer的約定，我們可以把它傳入Fprintf函數中；Fprintf函數執行字符串格式化的過程不會去關註ByteCounter正確的纍加結果的長度。
 
 ```go
 var c ByteCounter
 c.Write([]byte("hello"))
 fmt.Println(c) // "5", = len("hello")
-c = 0 // reset the counter
+c = 0          // reset the counter
 var name = "Dolly"
 fmt.Fprintf(&c, "hello, %s", name)
 fmt.Println(c) // "12", = len("hello, Dolly")
@@ -69,11 +73,12 @@ fmt.Println(c) // "12", = len("hello, Dolly")
 
 ```go
 package fmt
+
 // The String method is used to print values passed
 // as an operand to any format that accepts a string
 // or to an unformatted printer such as Print.
 type Stringer interface {
-    String() string
+	String() string
 }
 ```