Bump bootstrap from 4.0.0-beta to 4.0.0-beta.2

[dependabot]

Bumps bootstrap from 4.0.0-beta to 4.0.0-beta.2.

Release notes

Sourced from bootstrap's releases.

v4.0.0-beta.2

Beta 2 is here! Read the full ship list for details on what issues were closed and PRs merged.

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Highlights

• Improved Sass map customization with #23260. With this change, it's now possible to override specific key value pairs instead of resetting the entire map, ideal for color scheme customization.
• Restored grid .offset- modifiers in #23445. Originally our intent was to supplement this with our margin utilities, but we underestimated the appeal of fixed number column offsets.
• Remove unnecessary color from .badge, and it's associated $badge-color variable, in #23529.
• Rename grayscale function to gray to avoid breaking CSS native grayscale filter in #23579.
• Renamed .table-inverse, .thead-inverse, and .thead-default to .*-dark and .*-light, matching our color schemes used elsewhere in #23560.
• Responsive tables now generate classes for each grid breakpoint, meaning we've added .table-responsive-{sm,md,lg,xl} to the already present .table-responsive. You might need to adjust your usage depending on when you want a table to resize. See #22804.
• Include two new dist files which contain Popper.js inside bootstrap.bundle.js and bootstrap.bundle.min.js. See #23735.
• Dropped support for Bower as they've deprecated the package manager. See #23568.
• Switched breadcrumbs from float to flexbox in #23683.
• Added new CSS variables in #23761.
• Switched to Stylelint in #23572.
• New Theming page in the docs from #23611
• #23943: Changed the color-yiq from a mixin that included the color property to a function that returns a value, allowing you to use it for any CSS property. For example, instead of color-yiq([#000](https://github.com/twbs/bootstrap/issues/000)), you'd write color: color-yiq([#000](https://github.com/twbs/bootstrap/issues/000));.
• New and improved theming in #24429.

Commits

• fc94de5 typo
• 539510f add missing .
• 50a2345 new current_ruby-version var
• 0a1c70d update getting started docs too
• ab04e9b version number for homepage
• 2e9ab6c new hashes
• dbf5405 fix version number
• 73ade25 new shas
• cf00548 new version number
• 7b06b92 spelling changes to theming.md (#24444)
• Additional commits viewable in compare view

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[marclaporte]

Poor @dependabot seems lost in a time machine.

Bootstrap 4.0.0 was a long time ago.

It's time for Bootstrap 5.3!
#774