fix ojb -> obj (#402)

* 忽路->忽略

* 修复跳转链接错误

* fix Class.getInterface() -> Class.getInterfaces()

* 否者 -> 否则

* 编译期 -> 编译器 ，原文"the compiler will only allow you to say that the superclass reference is “some class that is a superclass of FancyToy” a"

* ierator -> iterator

* nextint -> nextInt

* fix 这句翻译第一反应没太看懂，结合原文和下面的例子优化了一下翻译

* fix ojb -> obj

docs/book/20-Generics.md

@@ -1409,7 +1409,7 @@ class Manipulator3 {
     private HasF obj;
     
     Manipulator3(HasF x) {
-        ojb = x;
+        obj = x;
     }
     
     public void manipulate() {