message: fix(package): update hard-source-webpack-plugin to version 0.6.4
  Closes
diff: "ethereumjs-util": "5.1.5",
  "ethereumjs-wallet": "0.6.0",
  "font-awesome": "4.7.0",
  - "hard-source-webpack-plugin": "0.6.1",
  + "hard-source-webpack-plugin": "0.6.4",
  "hdkey": "0.8.0",
  "idna-uts46": "1.1.0",
  "jsonschema": "1.2.2",
  