Update translation of zh_CN

Correct some spelling and grammar mistakes in zh_CN
Modify punctuations according to Chinese customs

BTW, Why will I get a 'language-mixed' version of TM (see the screenshot below) even though the i10n file doesn't contain any errors?
![screen](https://cloud.githubusercontent.com/assets/2819727/3007056/cccff8da-de67-11e3-8aff-177d05b0534f.PNG)


Signed-off-by: Harry Chen <373685963@qq.com>