Update dependency @shelf/eslint-config to v0.3.9

Author: renovate-bot

package.json

@@ -37,7 +37,7 @@
     "dynamodb-local": "0.0.29"
   },
   "devDependencies": {
-    "@shelf/eslint-config": "0.3.7",
+    "@shelf/eslint-config": "0.3.9",
     "eslint": "5.16.0",
     "husky": "2.5.0",
     "jest": "24.8.0",