fix: upgrade multiple dependencies with Snyk

Snyk has created this PR to upgrade:
  - react from 16.12.0 to 16.13.0.
    See this package in NPM: https://www.npmjs.com/package/react
  - react-dom from 16.12.0 to 16.13.0.
    See this package in NPM: https://www.npmjs.com/package/react-dom

See this project in Snyk:
https://app.snyk.io/org/creyd-github-marketplace/project/7687a902-5880-4dba-8e64-1ed2c0311711?utm_source=github&utm_medium=upgrade-pr

package.json

@@ -17,8 +17,8 @@
     "dateformat": "^3.0.3",
     "gatsby": "^2.18.12",
     "gatsby-plugin-manifest": "^2.2.38",
-    "react": "^16.12.0",
-    "react-dom": "^16.12.0"
+    "react": "^16.13.0",
+    "react-dom": "^16.13.0"
   },
   "devDependencies": {
     "prettier": "^1.19.1",