Bump gatsby from 3.0.4 to 3.1.0

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 3.0.4 to 3.1.0.
- [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@3.0.4...gatsby@3.1.0)

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

package.json

@@ -33,7 +33,7 @@
     "@types/react-helmet": "^6.1.0",
     "add": "^2.0.6",
     "classnames": "^2.2.6",
-    "gatsby": "^3.0.4",
+    "gatsby": "^3.1.0",
     "gatsby-image": "^3.1.0",
     "gatsby-plugin-feed": "^3.0.0",
     "gatsby-plugin-google-analytics": "^3.1.0",