build(deps): bump gatsby-remark-responsive-iframe in /docs

Bumps [gatsby-remark-responsive-iframe](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-remark-responsive-iframe) from 5.11.0 to 5.13.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-remark-responsive-iframe/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-remark-responsive-iframe@5.13.0/packages/gatsby-remark-responsive-iframe)

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

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

docs/package.json

@@ -31,7 +31,7 @@
     "gatsby-remark-external-links": "^0.0.4",
     "gatsby-remark-images": "^6.11.1",
     "gatsby-remark-mermaid": "^2.1.0",
-    "gatsby-remark-responsive-iframe": "^5.11.0",
+    "gatsby-remark-responsive-iframe": "^5.13.0",
     "gatsby-source-filesystem": "^4.13.0",
     "gatsby-transformer-remark": "^5.11.1",
     "gatsby-transformer-sharp": "^4.13.0",