chore(package): update webpack to version 3.4.0

Closes #14

Author: greenkeeper[bot]

package.json

@@ -36,6 +36,6 @@
     "react-cosmos-webpack": "^2.0.0-beta.14",
     "style-loader": "~0.18.2",
     "webdriverio": "^4.6.2",
-    "webpack": "~2.3.2"
+    "webpack": "~3.4.0"
   }
 }