Bump gatsby from 2.3.5 to 2.17.1

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 2.3.5 to 2.17.1.
- [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@2.3.5...gatsby@2.17.1)

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

Author: dependabot-preview[bot]