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Bump elliptic from 6.4.1 to 6.5.3

Bump websocket-extensions from 0.1.3 to 0.1.4

Bump lodash from 4.17.15 to 4.17.20

Bump jquery from 3.4.1 to 3.5.0

Bump dot-prop from 4.2.0 to 4.2.1

Bumps [elliptic](https://github.com/indutny/elliptic) from 6.4.1 to 6.5.3.
- [Release notes](https://github.com/indutny/elliptic/releases)
- [Commits](https://github.com/indutny/elliptic/compare/v6.4.1...v6.5.3

)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [websocket-extensions](https://github.com/faye/websocket-extensions-node) from 0.1.3 to 0.1.4.
- [Release notes](https://github.com/faye/websocket-extensions-node/releases)
- [Changelog](https://github.com/faye/websocket-extensions-node/blob/master/CHANGELOG.md)
- [Commits](https://github.com/faye/websocket-extensions-node/compare/0.1.3...0.1.4

)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [lodash](https://github.com/lodash/lodash) from 4.17.15 to 4.17.20.
- [Release notes](https://github.com/lodash/lodash/releases)
- [Commits](https://github.com/lodash/lodash/compare/4.17.15...4.17.20

)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [dot-prop](https://github.com/sindresorhus/dot-prop) from 4.2.0 to 4.2.1.
- [Release notes](https://github.com/sindresorhus/dot-prop/releases)
- [Commits](https://github.com/sindresorhus/dot-prop/compare/v4.2.0...v4.2.1

)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [jquery](https://github.com/jquery/jquery) from 3.4.1 to 3.5.0.
- [Release notes](https://github.com/jquery/jquery/releases)
- [Commits](https://github.com/jquery/jquery/compare/3.4.1...3.5.0

)
Signed-off-by: dependabot[bot] <support@github.com>

Remove deprecated `background-image-svg()` mixin calls

Deprecated in MW 1.35 and to be removed in MW 1.36.
See https://phabricator.wikimedia.org/T248062 for more information.

Use hook to add body attributes