change github.com links to github.io links

[alifeee]

github.com is no longer used for GitHub pages sites

please see https://github.blog/2013-04-05-new-github-pages-domain-github-io/

github.io is the correct link

example:

• old, broken link: http://dhotson.github.com/springy/demo-simple.html
• new, fixed link: http://dhotson.github.io/springy/demo-simple.html