fix mis-translation private<-->public

 public.key is "公開鍵" and private.key is "秘密鍵" in Japanese.
Update 01-chapter3.markdown

笔误修改

原文：You can take the changes on client that aren’t on server (C8 and C9) and replay them on your master branch by using the --onto option of git rebase
Merge pull request #726 from diceit/4-7

fix mis-translation private<-->public
Merge pull request #727 from lusecond/master

[zh] Update 01-chapter3.markdown
[it] Reviewed "Moving Files"
[it] Reviewed "Viewing the Commit History"
[it] Edited chapter 6

Copied english source (to be translated) and reviewed part of the translation