update minimum required webpack version

Author: SpaceK33z

package.json

@@ -40,7 +40,7 @@
     "style-loader": "~0.13.0",
     "supertest": "^2.0.0",
     "url-loader": "~0.5.6",
-    "webpack": "^2.1.0-beta.1"
+    "webpack": "^2.1.0-beta.26"
   },
   "license": "MIT",
   "repository": {