chore(deps): bump gatsby-source-filesystem from 5.14.0 to 5.15.0 (#835)

Bumps [gatsby-source-filesystem](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-source-filesystem) from 5.14.0 to 5.15.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-source-filesystem/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-source-filesystem)

---
updated-dependencies:
- dependency-name: gatsby-source-filesystem
  dependency-version: 5.15.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

package-lock.json

@@ -34,7 +34,7 @@
     "gatsby-remark-autolink-headers": "^6.0.0",
     "gatsby-remark-classes": "^1.0.2",
     "gatsby-remark-prismjs": "^7.15.0",
-    "gatsby-source-filesystem": "^5.0.0",
+    "gatsby-source-filesystem": "^5.15.0",
     "gatsby-transformer-json": "^5.15.0",
     "gatsby-transformer-remark": "^6.13.1",
     "gatsby-transformer-sharp": "^5.15.0",