Update dependency gatsby-transformer-remark to v5 [SECURITY]

Author: renovate[bot]

package.json

@@ -24,7 +24,7 @@
     "gatsby-remark-images": "3.0.11",
     "gatsby-remark-prismjs": "3.2.9",
     "gatsby-source-filesystem": "^1.4.12",
-    "gatsby-transformer-remark": "^1.7.7",
+    "gatsby-transformer-remark": "^5.0.0",
     "just-safe-get": "^2.0.0",
     "prismjs": "^1.15.0",
     "react": "^16.8.0",