fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-INFLIGHT-6095116

Author: snyk-bot

package.json

@@ -59,7 +59,7 @@
     "eslint-plugin-jsx-a11y": "^6.0.3",
     "eslint-plugin-react": "^7.7.0",
     "gatsby-plugin-styled-jsx": "^3.0.3",
-    "stylelint": "^9.1.1",
+    "stylelint": "^16.1.0",
     "stylelint-config-standard": "^18.2.0",
     "prettier": "^1.14.2"
   }