ch7: fix code format

ch7/ch7-05-1.md

@@ -8,22 +8,22 @@
 const debug = true
 
 func main() {
-    var buf *bytes.Buffer
-    if debug {
-        buf = new(bytes.Buffer) // enable collection of output
-    }
-    f(buf) // NOTE: subtly incorrect!
-    if debug {
-        // ...use buf...
-    }
+	var buf *bytes.Buffer
+	if debug {
+		buf = new(bytes.Buffer) // enable collection of output
+	}
+	f(buf) // NOTE: subtly incorrect!
+	if debug {
+		// ...use buf...
+	}
 }
 
 // If out is non-nil, output will be written to it.
 func f(out io.Writer) {
-    // ...do something...
-    if out != nil {
-        out.Write([]byte("done!\n"))
-    }
+	// ...do something...
+	if out != nil {
+		out.Write([]byte("done!\n"))
+	}
 }
 ```
 
@@ -31,7 +31,7 @@ func f(out io.Writer) {
 
 ```go
 if out != nil {
-    out.Write([]byte("done!\n")) // panic: nil pointer dereference
+	out.Write([]byte("done!\n")) // panic: nil pointer dereference
 }
 ```
 
@@ -46,7 +46,7 @@ if out != nil {
 ```go
 var buf io.Writer
 if debug {
-    buf = new(bytes.Buffer) // enable collection of output
+	buf = new(bytes.Buffer) // enable collection of output
 }
 f(buf) // OK
 ```