- Move 4.1 docs to 4.2
- Update versions everywhere to 4.1.3 with release script
- Manually bump the shorthand version in package.json
- Add 4.2 to the versions docs page
- Update some redirects
- Fix tests asset URLs
- Bump Nuget and more

This reverts commit af484dc1.

`shrink-to-fit=no` is not needed anymore - Apple removed the need for it from iOS9.3 onwards

See https://www.scottohara.me/blog/2018/12/11/shrink-to-fit.html and https://github.com/h5bp/html5-boilerplate/issues/2102

Broken after 787441d4.

Having it uppercase doesn't offer anything and the lowercase version slightly improves gzip compression.

According to the docs, you just need to apply the `navbar-nav` to an
`<ul>` tag in a list-based navbar. In fact, `navbar-nav` seems to
override all the css properties set by `nav`.

Also, `nav-item` class should be used only for `<li>` tags, or in
conjunction with `<a>` tags to entirely avoid the list-based approach.

This commit removes the redundant `nav` class from `navbar-nav` `<ul>`
tags, moves `nav-item` from `<a>` tags to `<li>` tags and properly
adds `nav-item` class to `<li>` tags where missing.

Refs:

* https://v4-alpha.getbootstrap.com/components/navs/
* https://v4-alpha.getbootstrap.com/components/navbar/#nav

Closes https://github.com/twbs/bootstrap/issues/21635

* Remove IE compatibility mode meta tag from docs, examples, and JS tests as we no longer support IE9 and IE8
* update and remove some IE bits from our supported browser page
* update introduction.md to match
* reword starter template intro

* Throw error when a plugin is in transition
* Add unit tests about plugins in transition

[skip sauce]

See also https://bugzilla.mozilla.org/show_bug.cgi?id=1228802

add modal my gawd

Fixes #15136.
Closes #15345.
Closes #15314.
Refs #14724, #14927.