fix: coding style and file format for all example.

eBook/examples/chapter_12/filecopy.go

@@ -1,29 +1,29 @@
-// filecopy.go
-package main
-
-import (
-	"fmt"
-	"io"
-	"os"
-)
-
-func main() {
-	CopyFile("target.txt", "source.txt")
-	fmt.Println("Copy done!")
-}
-
-func CopyFile(dstName, srcName string) (written int64, err error) {
-	src, err := os.Open(srcName)
-	if err != nil {
-		return
-	}
-	defer src.Close()
-
-	dst, err := os.OpenFile(dstName, os.O_WRONLY|os.O_CREATE, 0644)
-	if err != nil {
-		return
-	}
-	defer dst.Close()
-
-	return io.Copy(dst, src)
-}
+// filecopy.go
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+func main() {
+	CopyFile("target.txt", "source.txt")
+	fmt.Println("Copy done!")
+}
+
+func CopyFile(dstName, srcName string) (written int64, err error) {
+	src, err := os.Open(srcName)
+	if err != nil {
+		return
+	}
+	defer src.Close()
+
+	dst, err := os.OpenFile(dstName, os.O_WRONLY|os.O_CREATE, 0644)
+	if err != nil {
+		return
+	}
+	defer dst.Close()
+
+	return io.Copy(dst, src)
+}