move Grunt info from README into HTML docs

Fixes #13470
Merge pull request #13531 from twbs/grunt-html-docs

move Grunt info from README into HTML docs
Update .travis.yml
Remove outdated rtl nav links
Merge pull request #13536 from Quy/master

Remove outdated rtl nav links
grunt dist
Customizer: make utilities.less inclusion mandatory

Fixes #13305.
Merge pull request #13543 from twbs/fix-13305

Customizer: make utilities.less inclusion mandatory
Merge branch 'master' of github.com:twbs/bootstrap into aria-describedby-tooltip-13480

Conflicts:
	dist/js/bootstrap.min.js
	docs/dist/js/bootstrap.min.js

Recompiled the assets