Reset github ssh auth

It’s a reminder for myself as I have several ssh key pairs.

Set ssh public key on github page. Mine is pub.bak.
Config private key in .ssh/config. Mine is id_rsa.bak.
```
Host github.com
  IdentityFile ~/.ssh/id_rsa.bak
```
Remove http origin if u have one, coz github doesn’t support http auth with username and password now. Execute git remote remove origin and add the new ssh origin.