chore(package): update eslint to version 5.15.0

Closes #262

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
   },
   "devDependencies": {
     "chai": "~4.1.0",
-    "eslint": "^4.0.0",
+    "eslint": "^5.15.0",
     "eslint-config-standard": "^11.0.0",
     "eslint-plugin-import": "^2.2.0",
     "eslint-plugin-node": "^6.0.0",