restore demo dependencies

Author: Hamms

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "build": "webpack -p",
     "build:dev": "webpack --progress --colors --mode=development",
-    "build:demo": "webpack --config demo/webpack.config.js",
+    "build:demo": "webpack --config demo/webpack.config.js -p",
     "lint": "eslint --ext .js src/ test",
     "postversion": "git push && git push --tags && npm publish",
     "preversion": "npm run test",
@@ -35,6 +35,8 @@
     "codecov": "^3.0.0",
     "eslint": "^3.19.0",
     "eslint-plugin-babel": "^4.1.2",
+    "file-loader": "^1.1.11",
+    "html-webpack-plugin": "^3.2.0",
     "jest": "^22.1.3",
     "webpack": "^4.8.1",
     "webpack-cli": "^2.1.3"