Convert http links to https (#8287)

* Convert http links to https

* Fix remaining links

certbot-dns-digitalocean/docs/conf.py

@@ -93,7 +93,7 @@ todo_include_todos = False
 # a list of builtin themes.
 #
 
-# http://docs.readthedocs.org/en/latest/theme.html#how-do-i-use-this-locally-and-on-read-the-docs
+# https://docs.readthedocs.io/en/stable/faq.html#i-want-to-use-the-read-the-docs-theme-locally
 # on_rtd is whether we are on readthedocs.org
 on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
 if not on_rtd:  # only import and set the theme if we're building docs locally