Build(deps-dev): bump gatsby from 3.3.1 to 3.4.0

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 3.3.1 to 3.4.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/compare/gatsby@3.3.1...gatsby@3.4.0)

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