Merge pull request #106 from dbarobin/master

[Typo] Fix wrong double quotation marks

eBook/04.4.md

@@ -80,7 +80,7 @@ var str string = "Go says hello to the world!"
 ```go
 var a = 15
 var b = false
-var str = “Go says hello to the world!”
+var str = "Go says hello to the world!"
 ```
 
 或：