match project's style check

Don't reference `Tether` via attachment to `window`, with the update one can import bootstrap providing the dependencies in webpack with:

```
new webpack.ProvidePlugin({
  $: 'jquery',
  jQuery: 'jquery',
  Tether: 'tether',
});
```

Then inside one's own bootstrap/globals, `import 'bootstrap';` will simply work, and $/jQuery can be used from there.

I had wanted to do this, but also expose jQuery, Tether, etc when in development build in my code, but if I provide `window.Tether`, I can't then expose it to the outside...

Add jQuery and Tether to npm dependencies

Mention https://webkit.org/b/153856 in the docs

Refs #14839, #19088
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Remove iOS virtual keyboard bug section from docs

Closes #19532
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CONTRIBUTING.md: Prohibit "+1" comments in favor of reactions
[ci skip]

Jekyll 3.x has it as a dependency already.

Make hound fail on violations

Refs https://github.com/blog/2119-add-reactions-to-pull-requests-issues-and-comments
Refs https://github.com/dear-github/dear-github/issues/141#issuecomment-195106918
[ci skip]

Wall of Browser Bugs: Stop mentioning IE11

Sounds like IE11 isn't getting non-critical fixes anymore, so there's no point in mentioning it (just like there's no point in mentioning IE10).
Help us, Edge-Wan Kenobi! You're our only hope.
[ci skip]

http://bugzil.la/1139853 was resolved as a duplicate of http://bugzil.la/924068
Refs #15990
[ci skip]

[ci skip]

Add native title tooltip IE11/Edge bug to wall of browser bugs

Travis CI: Remove now-unused $GEMDIR env var

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Remove the now unused btoa dependency.

[skip sauce]

[ci skip]

Also switch to `^`.

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The modal backdrop positioning bug related to iOS' virtual keyboard doesn't seem to reproduce in iOS 8.0+.
(Possibly as a side-effect of https://bugs.webkit.org/show_bug.cgi?id=153224 )
Refs #9023
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Docs: Link directly to printing-related browser bugs

* https://bugs.chromium.org/p/chromium/issues/detail?id=273306
* https://bugs.webkit.org/show_bug.cgi?id=138192
[skip sauce]

Docs: Add link to Chrome bug regarding `body { overflow: hidden; }`

https://bugs.chromium.org/p/chromium/issues/detail?id=175502
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Introduction for using table-reflow

For consistency with the rest of the file
[ci skip]

Neutralize link styles for placeholder links/named anchors

Remove Wall of Browser Bugs entry for #19390

Refs https://bugzilla.mozilla.org/show_bug.cgi?id=1217012
Refs #19393
[ci skip]

Add Wall of Browser Bugs entry for #19390

https://bugzilla.mozilla.org/show_bug.cgi?id=1253468
Closes #19390
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Added colon before enumeration
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[skip validator]
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