Bump gatsby-plugin-sharp from 3.12.0 to 3.13.0 in /packages/website

Bumps [gatsby-plugin-sharp](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-sharp) from 3.12.0 to 3.13.0.
- [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@3.13.0/packages/gatsby-plugin-sharp)

---
updated-dependencies:
- dependency-name: gatsby-plugin-sharp
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

packages/website/package.json

@@ -26,7 +26,7 @@
     "gatsby-plugin-purgecss": "^6.0.2",
     "gatsby-plugin-react-helmet": "^4.13.0",
     "gatsby-plugin-robots-txt": "^1.6.10",
-    "gatsby-plugin-sharp": "^3.12.0",
+    "gatsby-plugin-sharp": "^3.13.0",
     "gatsby-plugin-svgr": "^3.0.0-beta.0",
     "gatsby-remark-classes": "^1.0.0",
     "gatsby-remark-copy-linked-files": "^4.10.0",