chore(package): update eslint to version 6.0.1

Closes #99

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
     "marked": "https://github.com/observablehq/marked.git#94c6b946f462fd25db4465d71a6859183f86c57f"
   },
   "devDependencies": {
-    "eslint": "^5.10.0",
+    "eslint": "^6.0.1",
     "husky": "^2.3.0",
     "jsdom": "^15.1.0",
     "rollup": "^1.15.0",