Bump gatsby from 3.0.3 to 3.0.4

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 3.0.3 to 3.0.4.
- [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@3.0.3...gatsby@3.0.4)

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

package.json

@@ -11,7 +11,7 @@
     "@mdx-js/mdx": "^1.6.22",
     "@mdx-js/react": "^1.6.22",
     "babel-plugin-styled-components": "^1.12.0",
-    "gatsby": "^3.0.3",
+    "gatsby": "^3.0.4",
     "gatsby-core-utils": "^2.0.0",
     "gatsby-image": "^3.0.0",
     "gatsby-plugin-feed": "^3.0.0",