Fix a small bug

[ruohai0925]

https://github.com/Light-City/CPlusPlusThings/tree/master/basic_content/sizeof#4%E5%8E%9F%E5%88%994%E4%B8%8E5

原则4与5中

有一句代码应该是

class C1:public A1

而不是

class C1:public A

[stoody-dev]

assign me 我会处理这个问题

[laialaodi]

建议直接 PR

[laialaodi]

@Light-City come and fix bug!