修正dial.go中格式化输出语句 (#411)

* 修正dial.go例子中格式化输出语句的错误

* 修正dial.go例子中格式化输出语句的错误

eBook/15.1.md

@@ -142,10 +142,10 @@ func main() {
 }
 func checkConnection(conn net.Conn, err error) {
 	if err != nil {
-		fmt.Printf("error %v connecting!")
+		fmt.Printf("error %v connecting!", err)
 		os.Exit(1)
 	}
-	fmt.Println("Connection is made with %v", conn)
+	fmt.Printf("Connection is made with %v\n", conn)
 }
 ```
 下边也是一个使用net包从socket中打开，写入，读取数据的例子：

eBook/examples/chapter_15/dial.go

@@ -17,8 +17,8 @@ func main() {
 }
 func checkConnection(conn net.Conn, err error) {
 	if err != nil {
-		fmt.Printf("error %v connecting!")
+		fmt.Printf("error %v connecting!", err)
 		os.Exit(1)
 	}
-	fmt.Println("Connection is made with %v", conn)
+	fmt.Printf("Connection is made with %v\n", conn)
 }