l10n: zh_CN: for git v2.20.0 l10n round 1 to 3

Translate 257 new messages (4187t0f0u) for git 2.20.0.

Reviewed-by: Zhou Fangyi <fangyi.zhou@yuriko.moe>
Reviewed-by: 依云 <lilydjwg@gmail.com>
Signed-off-by: Jiang Xin <worldhello.net@gmail.com>