chore(package): update eslint to version 5.15.0

Closes #36

Author: greenkeeper[bot]

package.json

@@ -59,7 +59,7 @@
     "esdoc-ecmascript-proposal-plugin": "^1.0.0",
     "esdoc-importpath-plugin": "^1.0.1",
     "esdoc-standard-plugin": "^1.0.0",
-    "eslint": "^4.15.0",
+    "eslint": "^5.15.0",
     "eslint-config-happiness": "^10.2.1",
     "eslint-plugin-import": "^2.7.0",
     "eslint-plugin-node": "^5.1.1",