fix(package): add webpack >= v4.0.0 (peerDependencies) (#245)

Author: ryanclark

package.json

@@ -37,7 +37,7 @@
   },
   "peerDependencies": {
     "less": "^2.3.1",
-    "webpack": "^2.0.0 || ^3.0.0"
+    "webpack": "^2.0.0 || ^3.0.0 || ^4.0.0"
   },
   "devDependencies": {
     "babel-cli": "^6.24.0",