Fix TypeError in CleanWebpackPlugin instantiation (#185)

Fix "TypeError: CleanWebpackPlugin is not a constructor" for clean-webpack-plugin >= 3.0.0

webpack.dev.js

@@ -1,6 +1,6 @@
 const merge = require("webpack-merge");
 const path = require("path");
-const CleanWebpackPlugin = require("clean-webpack-plugin");
+const { CleanWebpackPlugin } = require('clean-webpack-plugin');
 const MiniCssExtractPlugin = require("mini-css-extract-plugin");
 
 const common = require("./webpack.common");