Bump gatsby from 2.21.9 to 3.10.2

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 2.21.9 to 3.10.2.
- [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@2.21.9...gatsby@3.10.2)

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

Author: dependabot-preview[bot]

packages/docs/package.json

@@ -25,7 +25,7 @@
     "@theme-ui/sidenav": "^0.3.1",
     "countries-list": "^2.4.3",
     "deepmerge": "^4.0.0",
-    "gatsby": "^2.13.48",
+    "gatsby": "^3.10.2",
     "gatsby-plugin-catch-links": "^2.1.2",
     "gatsby-plugin-mdx": "^1.0.22",
     "gatsby-plugin-react-helmet": "^3.1.3",