Bump gatsby-plugin-mdx from 2.0.1 to 2.1.0

Bumps [gatsby-plugin-mdx](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-mdx) from 2.0.1 to 2.1.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-mdx/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-plugin-mdx@2.1.0/packages/gatsby-plugin-mdx)

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

package.json

@@ -22,7 +22,7 @@
     "gatsby-plugin-google-tagmanager": "3.1.0",
     "gatsby-plugin-load-script": "1.1.0",
     "gatsby-plugin-manifest": "2.12.1",
-    "gatsby-plugin-mdx": "2.0.1",
+    "gatsby-plugin-mdx": "2.1.0",
     "gatsby-plugin-offline": "3.10.2",
     "gatsby-plugin-react-helmet": "3.10.0",
     "gatsby-plugin-sharp": "2.14.3",