Bump gatsby-remark-prismjs from 7.14.0 to 7.15.0

Bumps [gatsby-remark-prismjs](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-remark-prismjs) from 7.14.0 to 7.15.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-remark-prismjs/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-remark-prismjs)

---
updated-dependencies:
- dependency-name: gatsby-remark-prismjs
  dependency-version: 7.15.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

package-lock.json

@@ -25,7 +25,7 @@
     "gatsby-plugin-typography": "5.14.0",
     "gatsby-remark-copy-linked-files": "6.14.0",
     "gatsby-remark-images": "7.14.0",
-    "gatsby-remark-prismjs": "7.14.0",
+    "gatsby-remark-prismjs": "7.15.0",
     "gatsby-remark-responsive-iframe": "6.14.0",
     "gatsby-remark-smartypants": "6.15.0",
     "gatsby-source-filesystem": "5.14.0",