build(deps): bump gatsby-plugin-react-helmet in /docs

Bumps [gatsby-plugin-react-helmet](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-react-helmet) from 3.7.0 to 3.10.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-react-helmet/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-plugin-react-helmet@3.10.0/packages/gatsby-plugin-react-helmet)

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

Author: dependabot[bot]