fix(deps): update dependency bootstrap to v4.2.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change	References
bootstrap	dependencies	minor	4.1.3 -> 4.2.1	homepage, source

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Release Notes

twbs/bootstrap

### [`v4.2.1`](https://renovatebot.com/gh/twbs/bootstrap/releases/v4.2.1) [Compare Source](https://renovatebot.com/gh/twbs/bootstrap/compare/v4.1.3...v4.2.1) Bump to v4.2.1 to republish package on npm. [See v4.2.0 release notes](https://renovatebot.com/gh/twbs/bootstrap/releases/tag/v4.2.0) for changes introduced in v4.2.

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