zh-cn:Polish the keys

[modimobeikete]

I realized that something's strange in some translation so I polish it.

[Banane9]

Thanks! Please note that you will have to force update the master branch of your repo to this repository's, because I had to squash the commits. Otherwise, the list of commits you're trying to merge will become longer and longer. Ideally, your PRs should just be a few commits, and not all with the same title. You can ammend them, if you want to make work-in-progress commits.