fix: Images sed command parameter

[DieYiSu]

• The sed shell command which trying to replace jpgg with jpg
• The sed shell symbol in the command which trying to replace localhost:2368 with username and gh_repo.
• The Fixing Images step should be to do on the setup step.
• The master branch had been replaced with main branch by Github team at 2020/10, so you don't need to create master and gh-pages branch.