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fix #12708 by updating class names in the docs JS
avoid using .bs-* in example, & improve style
Use .bs-example-* instead of .bs-* in examples in docs

Refs #12610
Remove trailing space.
Merge pull request #12709 from twbs/bs-to-example-prefix

Use .bs-example-* instead of .bs-* in examples in docs
Fix scrollspy typo in docs.css
Merge pull request #12711 from ZDroid/scrollspy-typo

Fix scrollspy typo in docs.css