chore(package): update eslint to version 6.1.0

Closes #10

Author: greenkeeper[bot]

package.json

@@ -34,7 +34,7 @@
     "chai": "^4.1.1",
     "chai-as-promised": "^7.1.1",
     "coveralls": "^3.0.0",
-    "eslint": "^4.4.1",
+    "eslint": "^6.1.0",
     "js-promisify": "^1.1.0",
     "mocha": "^4.0.0",
     "nyc": "^11.1.0",