fix(package): add webpack >= v4.0.0 (peerDependencies) (#239)

Author: ai

package.json

@@ -61,7 +61,7 @@
     "webpack-defaults": "^1.6.0"
   },
   "peerDependencies": {
-    "webpack": "^2.0.0 || ^3.0.0"
+    "webpack": "^2.0.0 || ^3.0.0 || ^4.0.0"
   },
   "keywords": [
     "uglify",