fix sample code bug & reformat some sample code (#557)

* Update 01.2.md

删除：
- 不支持断言

* Formatting 问题5.1 code

* Formatting 问题5.3 code

* Correct the translation

- correct `令 v := map1[key1] 可以将 key1 对应的值赋值为 v` to `令 v := map1[key1] 可以将 key1 对应的值赋值给 v`

* Modified sample code

- Add `defer fi.Close()` on `示例 12.7`

* Reformatting some sample code on 13.3

* Update 14.2.md

* Reformatting the sample code.

eBook/13.3.md

@@ -14,7 +14,7 @@ func protect(g func()) {
 		log.Println("done")
 		// Println executes normally even if there is a panic
 		if err := recover(); err != nil {
-		log.Printf("run time panic: %v", err)
+			log.Printf("run time panic: %v", err)
 		}
 	}()
 	log.Println("start")