Update webpack configuration to work with webpack 4

package.json

@@ -37,7 +37,7 @@
     "eslint": "^4.16.0",
     "eslint-plugin-flowtype": "^2.42.0",
     "eslint-plugin-react": "^7.6.1",
-    "extract-text-webpack-plugin": "^3.0.2",
+    "extract-text-webpack-plugin": "next",
     "file-loader": "^1.1.5",
     "flow": "^0.2.3",
     "flow-bin": "^0.68.0",
@@ -47,8 +47,6 @@
     "lodash-webpack-plugin": "^0.11.4",
     "style-loader": "^0.20.1",
     "webpack": "^4.3.0",
-    "webpack-dev-server": "^3.1.1",
-    "webpack": "^4.3.0",
     "webpack-cli": "^2.0.13",
     "webpack-dev-server": "^3.1.1",
     "webpack-merge": "^4.1.1",

webpack.common.js

@@ -22,7 +22,7 @@ module.exports = {
     filename: '[name]-[chunkhash].js'
   },
   module: {
-    loaders: [
+    rules: [
       { test: /\.(woff2?|eot|ttf|svg)$/, loader: "file-loader" }
     ]
   },

webpack.dev.js

@@ -23,7 +23,7 @@ module.exports = env => merge(common, {
           path.resolve(__dirname, 'src/index.jsx')]
   },
   module: {
-    loaders: [
+    rules: [
       { test: /\.css$/, use: extractCSS },
       { test: /\.js(x)?$/, exclude: /node_modules/, loader: "babel-loader?cacheDirectory=true" }
     ]

webpack.prod.js

@@ -29,7 +29,7 @@ module.exports = env => merge(common, {
           path.resolve(__dirname, 'src/index.jsx')],
   },
   module: {
-    loaders: [
+    rules: [
       { test: /\.css$/, use: extractCSS },
       { test: /\.js(x)?$/, exclude: /node_modules/, loader: "babel-loader" }
     ]