chore(package): update eslint to version 6.4.0

Closes #21

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "compression": "1.6.2",
     "cross-env": "4.0.0",
     "css-loader": "^0.28.0",
-    "eslint": "^3.19.0",
+    "eslint": "^6.4.0",
     "eslint-plugin-import": "^2.2.0",
     "eslint-watch": "^3.0.1",
     "express": "4.15.2",