build(deps): bump gatsby-transformer-remark from 5.13.0 to 5.21.0 in /docs (golangci#3153)

Author: dependabot[bot]

docs/package-lock.json

@@ -33,7 +33,7 @@
     "gatsby-remark-mermaid": "^2.1.0",
     "gatsby-remark-responsive-iframe": "^5.21.0",
     "gatsby-source-filesystem": "^4.13.0",
-    "gatsby-transformer-remark": "^5.13.0",
+    "gatsby-transformer-remark": "^5.21.0",
     "gatsby-transformer-sharp": "^4.19.0",
     "gatsby-transformer-yaml": "^4.19.0",
     "polished": "^4.2.2",