Bump @cypress/webpack-dev-server from 1.8.3 to 1.8.4 (#305)

Bumps [@cypress/webpack-dev-server](https://github.com/cypress-io/cypress) from 1.8.3 to 1.8.4.
- [Release notes](https://github.com/cypress-io/cypress/releases)
- [Changelog](https://github.com/cypress-io/cypress/blob/develop/.releaserc.base.js)
- [Commits](https://github.com/cypress-io/cypress/compare/@cypress/webpack-dev-server-v1.8.3...@cypress/webpack-dev-server-v1.8.4)

---
updated-dependencies:
- dependency-name: "@cypress/webpack-dev-server"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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