chore(package): update eslint to version 6.1.0

Closes #59

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "browserify": "^14.5.0",
     "chai": "^4.1.2",
     "dirty-chai": "^2.0.1",
-    "eslint": "^4.11.0",
+    "eslint": "^6.1.0",
     "mocha": "^4.0.1",
     "publish-please": "^2.2.0"
   }