Update footer and documentation links to HTTPS (2factorauth#4656)

Updated footer links in layout files and the CONTRIBUTING.md file to link to HTTPS versions of sites.

CONTRIBUTING.md

@@ -153,7 +153,7 @@ The following is an example of a website that *supports* TFA:
       - hardware
       - totp
       - u2f
-    doc: http://www.google.com/intl/en-US/landing/2step/features.html
+    doc: https://www.google.com/intl/en-US/landing/2step/features.html
 ```
 
 #### Adding a site that *does not* support TFA
@@ -229,13 +229,13 @@ For context, check out the discussion in issue [#242][242].
 
 [242]: https://github.com/2factorauth/twofactorauth/issues/242
 [exclude]: /EXCLUSION.md
-[bundler]: http://bundler.io/
+[bundler]: https://bundler.io/
 [gemfile]: /Gemfile
-[jekyll]: http://jekyllrb.com/
+[jekyll]: https://jekyllrb.com/
 [travis]: https://travis-ci.org/2factorauth/twofactorauth
-[yaml]: http://www.yaml.org/
+[yaml]: https://yaml.org/
 [alexa]: https://www.alexa.com/siteinfo
 [github-tutorial]: https://help.github.com/articles/creating-and-deleting-branches-within-your-repository/
 [do-tutorial]: https://www.digitalocean.com/community/tutorials/how-to-use-git-branches
 [tinypng]: https://tinypng.com/
-[semantic-ui]: https://semantic-ui.com/elements/icon.html
+[semantic-ui]: https://semantic-ui.com/elements/icon.html

_layouts/default.html

@@ -47,7 +47,7 @@
   Made with tea
   <i class="leaf circular small icon"></i>
   by
-  <a href="http://joshldavis.com">Josh Davis</a>
+  <a href="https://joshldavis.com">Josh Davis</a>
   and love
   <i class="heart circular small icon"></i>
   from some awesome

_layouts/secondary.html

@@ -65,7 +65,7 @@ <h2>Two Factor Auth (2FA)</h2>
   Made with tea
   <i class="leaf circular small icon"></i>
   by
-  <a href="http://joshldavis.com">Josh Davis</a>
+  <a href="https://joshldavis.com">Josh Davis</a>
   and love
   <i class="heart circular small icon"></i>
   from some awesome