Use https where possible and fix redirects

Issues identified with the help of `awesome_bot` gem

README.md

@@ -1,6 +1,6 @@
 # Arbre - HTML Views in Ruby
 
-[Arbre][docs] makes it easy to generate HTML directly in Ruby. This gem was extracted from [Active Admin](https://github.com/activeadmin/active_admin).
+[Arbre][docs] makes it easy to generate HTML directly in Ruby. This gem was extracted from [Active Admin](https://github.com/activeadmin/activeadmin).
 
 [![Version         ][rubygems_badge]][rubygems]
 [![Github Actions  ][actions_badge]][actions]
@@ -31,13 +31,13 @@ Subscribe to [Tidelift][tidelift] to support Arbre and get licensing assurances
 Please use the Tidelift security contact to [report a security vulnerability][Tidelift security contact].
 Tidelift will coordinate the fix and disclosure.
 
-[rubygems_badge]: http://img.shields.io/gem/v/arbre.svg
+[rubygems_badge]: https://img.shields.io/gem/v/arbre.svg
 [rubygems]: https://rubygems.org/gems/arbre
 [actions_badge]: https://github.com/activeadmin/arbre/workflows/ci/badge.svg
 [actions]: https://github.com/activeadmin/arbre/actions
-[tidelift_badge]: https://tidelift.com/badges/github/activeadmin/arbre
+[tidelift_badge]: https://tidelift.com/badges/package/rubygems/arbre
 [tidelift]: https://tidelift.com/subscription/pkg/rubygems-arbre?utm_source=rubygems-arbre&utm_medium=referral&utm_campaign=readme
 
 [docs]: https://activeadmin.github.io/arbre/
-[stackoverflow]: http://stackoverflow.com/questions/tagged/arbre
+[stackoverflow]: https://stackoverflow.com/questions/tagged/arbre
 [Tidelift security contact]: https://tidelift.com/security

lib/arbre/html/tag.rb

@@ -7,7 +7,7 @@ module HTML
     class Tag < Element
       attr_reader :attributes
 
-      # See: http://www.w3.org/html/wg/drafts/html/master/syntax.html#void-elements
+      # See: https://html.spec.whatwg.org/multipage/syntax.html#void-elements
       SELF_CLOSING_ELEMENTS = [ :area, :base, :br, :col, :embed, :hr, :img, :input, :keygen, :link,
                             :menuitem, :meta, :param, :source, :track, :wbr ]