Outdated and Broken links to be removed/updated

[leesheppard]

There's numerous links that are no longer valid and should be removed/edited with working links where possible.

e.g. https://rails-girls-map.herokuapp.com/

Some links on this page are broken for e.g. https://railsgirls.com/materials.html

[runlevel5]

Pull Request to fix those links are welcome