message: add copy-webpack-plugin
diff: "classnames": "^2.2.5",
  "clean-webpack-plugin": "^0.1.19",
  "connect-history-api-fallback": "^1.5.0",
  + "copy-webpack-plugin": "^4.6.0",
  "core-js": "^2.5.7",
  "cross-env": "^5.2.0",
  "css-loader": "^0.28.11",
  "bitcoinjs-message": "^2.0.0",
  "coininfo": "git+https://github.com/cryptocoinjs/coininfo.git",
  "copy-dir-cli": "0.0.3",
  - "copy-webpack-plugin": "^4.6.0",
  "ethereum-input-data-decoder": "0.0.12",
  "firebase": "^5.5.9",
  "ipfs": "^0.33.1",
  