W012 isn't necessarily true in Bootstrap 4

[vtenfys]

A navbar's first child shouldn't be a container if the navbar is inside a container itself. See https://getbootstrap.com/docs/4.0/examples/navbars/ - the light floating navbars do not have a container inside them as this would result in extra unwanted padding.

[cvrebert]

Bootlint has not yet been updated for Bootstrap 4. Only Bootstrap 3 is currently supported.

[Herst]

See also #304.

[pjmcdermott]

The container documentation for Bootstrap 3 says:

Note that, due to padding and more, neither container is nestable.

There is a good explanation of why in The Subtle Magic Behind Why the Bootstrap 3 Grid Works.

So I don't think W012 is true even in Bootstrap 3. This issue should be re-opened.

I suspect the issues is that navbar-* elements should be in a container, but this does not mean that a navbar's 1st child element must be a container.