fix(package): add webpack >= v4.0.0 (peerDependencies) (#67)

Author: lencioni

package.json

@@ -21,7 +21,7 @@
   },
   "homepage": "https://github.com/webpack-contrib/expose-loader",
   "peerDependencies": {
-    "webpack": "^2.0.0 || ^3.0.0"
+    "webpack": "^2.0.0 || ^3.0.0 || ^4.0.0"
   },
   "engines": {
     "node": ">= 4.3 < 5.0.0 || >= 5.10"