modify reason: wrong double quotes format (#356)

eBook/13.2.md

@@ -37,11 +37,11 @@ runtime.goexit /go/src/pkg/runtime/proc.c:148
 一个检查程序是否被已知用户启动的具体例子：
 
 ```go
-var user = os.Getenv(“USER”)
+var user = os.Getenv("USER")
 
 func check() {
-	if user == “” {
-		panic(“Unknown user: no value for $USER”)
+	if user == "" {
+		panic("Unknown user: no value for $USER")
 	}
 }
 ```
@@ -52,7 +52,7 @@ func check() {
 
 ```go
 if err != nil {
-	panic(“ERROR occurred:” + err.Error())
+	panic("ERROR occurred:" + err.Error())
 }
 ```
 

eBook/13.3.md

@@ -11,13 +11,13 @@
 ```go
 func protect(g func()) {
 	defer func() {
-		log.Println(“done”)
+		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”)
+	log.Println("start")
 	g() //   possible runtime-error
 }
 ```