修改例子的输出错误 (#559)

eBook/13.4.md

@@ -106,11 +106,11 @@ func main() {
 Parsing "1 2 3 4 5":
   [1 2 3 4 5]
 Parsing "100 50 25 12.5 6.25":
-  pkg parse: error parsing "12.5" as int
+  pkg: pkg parse: error parsing "12.5" as int
 Parsing "2 + 2 = 4":
-  pkg parse: error parsing "+" as int
+  pkg: pkg parse: error parsing "+" as int
 Parsing "1st class":
-  pkg parse: error parsing "1st" as int
+  pkg: pkg parse: error parsing "1st" as int
 Parsing "":
   pkg: no words to parse
 ```