update chinese translation for 2.1

this is a team work by the following people:
  Beaver Xu <xtfllbl@hotmail.com>
  cch123 <cao1988228@163.com>
  shiroki <shiroki@cuteqt.com>
  Rei <chloerei@gmail.com>

Merge-request: 210

share/qtcreator/translations/translations.pro

 include(../../../qtcreator.pri)
 
-LANGUAGES = de fr ja pl ru
+LANGUAGES = de fr ja pl ru zh_CN
 
 # var, prepend, append
 defineReplace(prependAll) {