Fix links to GitHub repo for spencerlyon2/hugo_gh_blog

Hello,

The `github_pages_blog.md` tutorial mentioned links to the git repository of "spencerlyon2/hugo_gh_blog" however it was linking to the page itself (i.e. http://spencerlyon2.github.io/hugo_gh_blog ).

This commit replace those links with links to https://github.com/spencerlyon2/hugo_gh_blog