fix(theme) use .concat for old node versions

Author: bertho-zero

src/theme/buildExtractStylesLoader.js

@@ -11,7 +11,7 @@ function encodeLoader(loader) {
   if (typeof loader.options !== 'undefined') {
     const query = Object
       .keys(loader.options)
-      .map((param) => `${encodeURIComponent(param)}=${encodeURIComponent(loader.options[param])}`)
+      .map(param => `${encodeURIComponent(param)}=${encodeURIComponent(loader.options[param])}`)
       .join('&');
     return `${loader.loader}?${query}`;
   }
@@ -28,7 +28,7 @@ module.exports = function buildExtractStylesLoader(loaders) {
 
   const restLoaders = loaders
     .slice(2)
-    .map((loader) => {
+    .map(loader => {
       if (typeof loader === 'string') {
         return loader;
       }
@@ -37,7 +37,6 @@ module.exports = function buildExtractStylesLoader(loaders) {
 
   return [
     extractTextLoader,
-    fallbackLoader,
-    ...restLoaders,
-  ].join('!');
+    fallbackLoader
+  ].concat(restLoaders).join('!');
 };