Bump gatsby-transformer-sharp from 2.2.21 to 2.5.7

Bumps [gatsby-transformer-sharp](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-transformer-sharp) from 2.2.21 to 2.5.7.
- [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@2.5.7/packages/gatsby-transformer-sharp)

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

Author: dependabot-preview[bot]

package.json

@@ -14,7 +14,7 @@
     "gatsby-plugin-react-helmet": "^3.1.21",
     "gatsby-plugin-sharp": "^2.2.27",
     "gatsby-source-filesystem": "^2.1.57",
-    "gatsby-transformer-sharp": "^2.2.21",
+    "gatsby-transformer-sharp": "^2.5.7",
     "gatsby-transformer-yaml": "^2.2.12",
     "postcss-custom-media": "^7.0.8",
     "postcss-nested": "^4.1.2",