fix(deps): bump react-helmet in /gatsby-theme-sputnik

Bumps [react-helmet](https://github.com/nfl/react-helmet) from 5.2.1 to 6.0.0.
- [Release notes](https://github.com/nfl/react-helmet/releases)
- [Changelog](https://github.com/nfl/react-helmet/blob/master/CHANGELOG.md)
- [Commits](https://github.com/nfl/react-helmet/commits/6.0.0)

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

gatsby-theme-sputnik/package.json

@@ -51,7 +51,7 @@
     "gatsby-plugin-robots-txt": "^1.5.0",
     "gatsby-plugin-sitemap": "^2.2.14",
     "modern-normalize": "^0.6.0",
-    "react-helmet": "^5.2.1",
+    "react-helmet": "^6.0.0",
     "typeface-lato": "0.0.75"
   },
   "peerDependencies": {