chore(package): update eslint to version 6.1.0

Closes #70

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
   },
   "devDependencies": {
     "chai": "^4.1.2",
-    "eslint": "^4.14.0",
+    "eslint": "^6.1.0",
     "eslint-config-tschaub": "^10.0.0",
     "gulp": "^3.9.1",
     "mocha": "^4.1.0",