build(deps): bump gatsby-plugin-manifest from 2.9.1 to 2.12.0 in /docs (#1704)

Author: dependabot[bot]

docs/package-lock.json

@@ -17,7 +17,7 @@
     "gatsby-plugin-catch-links": "^2.7.0",
     "gatsby-plugin-emotion": "^4.3.10",
     "gatsby-plugin-google-analytics": "^2.8.0",
-    "gatsby-plugin-manifest": "^2.9.1",
+    "gatsby-plugin-manifest": "^2.12.0",
     "gatsby-plugin-mdx": "^1.7.1",
     "gatsby-plugin-netlify": "^2.11.0",
     "gatsby-plugin-netlify-cache": "^1.2.0",