Remove .center-block class from the docs

[RyanZim]

.center-block was removed in #19102, but the docs still mention it.

Also this should be added to the Migration Guide.

[RyanZim]

It seems that this was updated in v4-dev docs/ on GitHub but hasn't been compiled to the gh-pages branch.

[XhmikosR]

@cvrebert: shouldn't we close this? I mean, gh-pages is from master so this is expected.

[cvrebert]

@XhmikosR There are still references to it in the docs:

bootstrap (v4-dev) $ ack center-block docs/
docs/assets/scss/_component-examples.scss
302:  .center-block:not(img) {

docs/content/images.md
63:  <img data-src="holder.js/200x200" class="img-rounded center-block" alt="A generic square placeholder image with rounded corners">
67:<img src="..." class="img-rounded center-block" alt="...">

docs/examples/carousel/index.html
132:          <img class="featurette-image img-fluid center-block" data-src="holder.js/500x500/auto" alt="Generic placeholder image">
144:          <img class="featurette-image img-fluid center-block" data-src="holder.js/500x500/auto" alt="Generic placeholder image">
156:          <img class="featurette-image img-fluid center-block" data-src="holder.js/500x500/auto" alt="Generic placeholder image">

docs/index.html
90:    <img class="img-fluid center-block" src="{{ site.baseurl }}/assets/img/bs-themes.png" alt="Bootstrap Themes" width="1024" height="388">

[XhmikosR]

Ah, that's why #19339 happens.

I'll try to have a look later.

[XhmikosR]

So, how do you want to proceed @cvrebert? m-x-auto doesn't set display: block. Should I add a custom class now?

[RyanZim]

#19343 is a feature request for .display-block, .display-inline, and display-inline-block. Why not include all of them while we're at it?

[cvrebert]

@XhmikosR I favor @RyanZim's suggestion.

[XhmikosR]

All right, I'll leave it to someone else for the time being.

[RyanZim]

Closing due to a0a157d.

[cvrebert]

<3