chore(package): update webpack to version 4.18.0

Author: greenkeeper[bot]

package.json

@@ -75,7 +75,7 @@
     "ts-node": "^5.0.1",
     "tslint": "^5.9.1",
     "typescript": "^2.7.2",
-    "webpack": "^4.1.1",
+    "webpack": "^4.18.0",
     "webpack-cli": "2.1.1",
     "yargs": "^11.0.0"
   },