Bump gatsby-plugin-sharp from 2.6.3 to 2.6.19

Bumps [gatsby-plugin-sharp](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-plugin-sharp) from 2.6.3 to 2.6.19.
- [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@2.6.19/packages/gatsby-plugin-sharp)

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

Author: dependabot-preview[bot]

package-lock.json

@@ -44,7 +44,7 @@
     "gatsby-plugin-manifest": "^2.4.3",
     "gatsby-plugin-react-helmet": "^3.3.2",
     "gatsby-plugin-sass": "^2.3.2",
-    "gatsby-plugin-sharp": "^2.6.3",
+    "gatsby-plugin-sharp": "^2.6.19",
     "gatsby-plugin-sitemap": "^2.4.11",
     "gatsby-plugin-typescript": "^2.4.3",
     "gatsby-remark-copy-linked-files": "^2.3.3",