[zh] Fix a missing word in 01-chapter6

"All the changes from your Rack project are merged in and ready to be committed locally." 
The word "and" is missed in the translation.
"归并" is a Chinese word which means "merge".
"并且" is a Chinese word which means "and".

*Perhaps* adding a comma between two words, like this:
```"所有 Rack 项目的变更都被归并，并且可以进行本地提交。"```
or not. I suppose Chinese people can read it(```被归并并且可以```) without any problem.