chore: webpack upgrade (#98)

* upgraded to webpack 4.x

* updated webpack

webpack.prod.js

@@ -0,0 +1,38 @@
+const webpack = require('webpack');
+const path = require('path');
+const CopyWebpackPlugin = require('copy-webpack-plugin');
+
+module.exports = {
+	mode: 'production',
+	entry: {
+		mergely: './src/mergely.js',
+	},
+	output: {
+		path: path.join(__dirname, 'lib'),
+		filename: './[name].js',
+		library: 'mergely',
+		libraryTarget: 'umd',
+		umdNamedDefine: true
+	},
+	module: {
+		rules: [{
+			test: /\.(js)$/,
+			exclude: /node_modules/,
+			use: ['babel-loader']
+		}]
+	},
+	resolve: {
+		extensions: ['.js']
+	},
+	externals: {
+		jquery: 'jQuery',
+		CodeMirror: 'CodeMirror'
+	},
+	plugins: [
+		new CopyWebpackPlugin([{
+			from: 'src/mergely.css',
+			to: 'mergely.css',
+			toType: 'file'
+		}])
+	]
+};