Fix broken/redirected links, moving to HTTPS where possible. (#20557)

docs/migration.md

@@ -41,7 +41,7 @@ Here are the big ticket items you'll want to be aware of when moving from v3 to
 
 - Dropped panels, thumbnails, and wells for a new all-encompassing component, cards.
 - Dropped the Glyphicons icon font. If you need icons, some options are:
-  - the upstream version of [Glyphicons](http://glyphicons.com/)
+  - the upstream version of [Glyphicons](https://glyphicons.com/)
   - [Octicons](https://octicons.github.com/)
   - [Font Awesome](https://fortawesome.github.io/Font-Awesome/)
 - Dropped the Affix jQuery plugin. We recommend using a `position: sticky` polyfill instead. [See the HTML5 Please entry](http://html5please.com/#sticky) for details and specific polyfill recommendations.
@@ -99,7 +99,7 @@ New to Bootstrap 4 is the Reboot, a new stylesheet that builds on Normalize with
 
 - Renamed `.btn-default` to `.btn-secondary`.
 - Dropped the `.btn-xs` class entirely as `.btn-sm` is proportionally much smaller than v3's.
-- The [stateful button](http://getbootstrap.com/javascript/#buttons-methods) feature of the `button.js` jQuery plugin has been dropped. This includes the `$().button(string)` and `$().button('reset')` methods. We advise using a tiny bit of custom JavaScript instead, which will have the benefit of behaving exactly the way you want it to.
+- The [stateful button](https://getbootstrap.com/javascript/#buttons-methods) feature of the `button.js` jQuery plugin has been dropped. This includes the `$().button(string)` and `$().button('reset')` methods. We advise using a tiny bit of custom JavaScript instead, which will have the benefit of behaving exactly the way you want it to.
   - Note that the other features of the plugin (button checkboxes, button radios, single-toggle buttons) have been retained in v4.
 
 ### Button group
@@ -129,7 +129,7 @@ New to Bootstrap 4 is the Reboot, a new stylesheet that builds on Normalize with
 
 ### Modal
 
-- The `remote` option (which could be used to automatically load and inject external content into a modal) and the corresponding `loaded.bs.modal` event were removed. We recommend instead using client-side templating or a data binding framework, or calling [jQuery.load](http://api.jquery.com/load/) yourself.
+- The `remote` option (which could be used to automatically load and inject external content into a modal) and the corresponding `loaded.bs.modal` event were removed. We recommend instead using client-side templating or a data binding framework, or calling [jQuery.load](https://api.jquery.com/load/) yourself.
 
 ### Navs
 
@@ -165,7 +165,7 @@ Dropped entirely for the new card component.
 - `.panel-default` removed and no replacement
 - `.panel-group` removed and no replacement. `.card-group` is not a replacement, it is different.
 - `.panel-heading` to `.card-header`
-- `.panel-title` to `.card-header`. Depending on the desired look, you may also want to use [heading elements or classes]({{ site.baseurl }}/content/typography/#headings) (e.g. `<h3>`, `.h3`) or bold elements or classes (e.g. `<strong>`, `<b>`, [`.font-weight-bold`]({{ site.baseurl }}/components/utilities/#font-weight-and-italics)). Note that `.card-title`, while similarly named, produces a different look than `.panel-title`.
+- `.panel-title` to `.card-header`. Depending on the desired look, you may also want to use [heading elements or classes]({{ site.baseurl }}/content/typography/#headings) (e.g. `<h3>`, `.h3`) or bold elements or classes (e.g. `<strong>`, `<b>`, [`.font-weight-bold`]({{ site.baseurl }}/utilities/typography/#font-weight-and-italics)). Note that `.card-title`, while similarly named, produces a different look than `.panel-title`.
 - `.panel-body` to `.card-block`
 - `.panel-footer` to `.card-footer`
 - `.panel-primary` to `.card-primary` and `.card-inverse` (or use `.bg-primary` on `.card-header`)