fix: remove redundant clean-webpack-plugin

Author: halfzebra

package.json

@@ -28,7 +28,6 @@
     "babel-runtime": "^6.26.0",
     "case-sensitive-paths-webpack-plugin": "^2.1.2",
     "chalk": "^2.3.1",
-    "clean-webpack-plugin": "^0.1.18",
     "cli-table": "0.3.1",
     "connect-history-api-fallback": "^1.5.0",
     "cosmiconfig": "^5.0.6",