Update grid-framework.less

The `when (@index = 1)` guards are not needed cause the mixins already only match on arity.
Fix #14936: Use correct left/right and margin on tooltip arrows
Fix typo

Corrected spelling of the word "elements"
Merge pull request #14967 from aaron-coding/patch-1

Fix typo
Add Wall of Browser Bugs entry for #14972
Merge pull request #14985 from twbs/14972-wall

Add Wall of Browser Bugs entry for #14972
Add #14868 to the compatibility docs
Add event.relatedTarget + `data-*` example to Modal docs

Fixes #14245
Use Jekyll data for Wall of Browser Bugs
Merge pull request #14989 from twbs/modal-relatedTarget-data-example

Add event.relatedTarget + `data-*` example to Modal docs
Remove duplicate code from Customizer/Gruntfile by sharing it
Merge pull request #14982 from twbs/grunt-customizer-share-common

Remove duplicate code from Customizer/Gruntfile by sharing it
Use autoprefixer for Customizer builds
Merge pull request #14980 from twbs/customizer-autoprefixer

Use autoprefixer for Customizer builds
Merge pull request #14987 from twbs/overengineer-wall-of-browser-bugs

Use Jekyll data for Wall of Browser Bugs
HTTPS for Apple Safari Radar in bugify filter
Add initialization examples to tooltip and popover "Opt-in functionality" callouts

Fixes #14950.
Closes #15015 by merging it.
Fix modal backdrop overlaying the modal's scrollbar

Fixes #14916.
Merge pull request #14938 from twbs/oh_arrow_where_art_thou

Fix #14936: Use correct left/right and margin on tooltip arrows
Deprecate diagonal tooltip classes