Typo Fix: Fix typo in chapter 3.2 about vector.

[mapleFU]

Change vetcor to vector in 3.2-chinese.md

[mapleFU]

In original post, this part is:

For those of you who aren’t aware of the issue, consider a stack<vector<int>>. Now, a vector is a dynamically sized container, so when you copy a vector the library has to allocate some more memory from the heap in order to copy the contents.

So I think it's vector rather than vetcor.

[xiaoweiChen]

感谢勘误！这的确是个笔误