Bump xml2js, gatsby-plugin-sharp and gatsby-transformer-sharp

Removes [xml2js](https://github.com/Leonidas-from-XIV/node-xml2js). It's no longer used after updating ancestor dependencies [xml2js](https://github.com/Leonidas-from-XIV/node-xml2js), [gatsby-plugin-sharp](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-sharp) and [gatsby-transformer-sharp](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-transformer-sharp). These dependencies need to be updated together.


Removes `xml2js`

Updates `gatsby-plugin-sharp` from 2.6.17 to 5.11.0
- [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@5.11.0/packages/gatsby-plugin-sharp)

Updates `gatsby-transformer-sharp` from 2.5.10 to 5.11.0
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-transformer-sharp/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-transformer-sharp@5.11.0/packages/gatsby-transformer-sharp)

---
updated-dependencies:
- dependency-name: xml2js
  dependency-type: indirect
- dependency-name: gatsby-plugin-sharp
  dependency-type: direct:production
- dependency-name: gatsby-transformer-sharp
  dependency-type: direct:production
...

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

package.json

@@ -11,9 +11,9 @@
     "gatsby-plugin-offline": "^3.2.0",
     "gatsby-plugin-react-helmet": "^3.3.0",
     "gatsby-plugin-sass": "^2.3.10",
-    "gatsby-plugin-sharp": "^2.6.0",
+    "gatsby-plugin-sharp": "^5.11.0",
     "gatsby-source-filesystem": "^2.3.0",
-    "gatsby-transformer-sharp": "^2.5.0",
+    "gatsby-transformer-sharp": "^5.11.0",
     "logrocket": "^1.0.10",
     "mobx": "^5.15.4",
     "node-sass": "^4.14.1",