Use Babel to transpile the client bundle to be compatible with old browsers (tested with iOS 9) (#4932)

.babelrc

@@ -0,0 +1,3 @@
+{
+    "presets": ["@babel/preset-env"]
+}

package.json

@@ -57,7 +57,10 @@
     "npm": "^6.4.1"
   },
   "dependencies": {
+    "@babel/core": "^7.5.5",
+    "@babel/preset-env": "^7.5.5",
     "async": "^0.9.2",
+    "babel-loader": "^8.0.6",
     "body-parser": "^1.19.0",
     "bootevent": "0.0.1",
     "braces": "^3.0.2",
@@ -125,5 +128,6 @@
     "webpack-bundle-analyzer": "^3.4.1",
     "webpack-dev-middleware": "^3.7.0",
     "webpack-hot-middleware": "^2.25.0"
-  }
+  },
+  "browserslist": "> 0.25%, not dead"
 }

webpack.config.js

@@ -68,7 +68,15 @@ pluginArray.push(new MomentLocalesPlugin({
   ],
 }));
 
-const rules = [{
+const rules = [
+  {
+    test: /\.(js|jsx)$/,
+    exclude: /node_modules/,
+    use: {
+      loader: "babel-loader"
+    }
+  },
+  {
     test: /\.(jpe?g|png|gif)$/i,
     loader: 'file-loader',
     query: {