Bump gatsby-plugin-sharp from 3.1.2 to 3.4.0

Bumps [gatsby-plugin-sharp](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-sharp) from 3.1.2 to 3.4.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-plugin-sharp/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-plugin-sharp@3.4.0/packages/gatsby-plugin-sharp)

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

package.json

@@ -75,7 +75,7 @@
     "gatsby-plugin-postcss": "^4.4.0",
     "gatsby-plugin-react-helmet": "^4.4.0",
     "gatsby-plugin-robots-txt": "^1.5.6",
-    "gatsby-plugin-sharp": "^3.1.2",
+    "gatsby-plugin-sharp": "^3.4.0",
     "gatsby-plugin-sitemap": "^3.1.0",
     "gatsby-transformer-sharp": "^3.4.0",
     "isomorphic-fetch": "^3.0.0",