message: build(webpack): lock webpack version
  webpack 4.29.* encountered a bug that using dynamic import grammar
diff: "@commitlint/config-conventional": "^7.1.2",
  "@types/jest": "^23.3.2",
  "@types/node": "^10.12.18",
  + "@vuepress/plugin-register-components": "^1.0.0-alpha.0",
  "autoprefixer": "^9.4.9",
  "babel-loader": "^8.0.5",
  "babel-preset-env": "^1.7.0",
  "vue-style-loader": "^4.1.2",
  "vue-template-compiler": "^2.6.10",
  "vuepress": "^1.0.0-alpha.46",
  - "webpack": "^4.28.4",
  + "webpack": "~4.28.4",
  "webpack-cli": "^3.3.0",
  "webpack-dev-middleware": "^3.6.0",
  "webpack-dev-server": "^3.2.1",
  