Fix language fallback in with-react-intl example (#8894)

The call to `accept.languages()` made the fallback not work.
When called e.g. with `Accept-Language: es-ES,es;q=0.9`, `locale` would contain `[ 'es-ES', 'es' ]` instead of `en`.

(See also: https://www.npmjs.com/package/accepts#languagelanguages )

examples/with-react-intl/server.js

@@ -46,7 +46,7 @@ const getMessages = locale => {
 app.prepare().then(() => {
   createServer((req, res) => {
     const accept = accepts(req)
-    const locale = accept.language(accept.languages(supportedLanguages)) || 'en'
+    const locale = accept.language(supportedLanguages) || 'en'
     req.locale = locale
     req.localeDataScript = getLocaleDataScript(locale)
     req.messages = dev ? {} : getMessages(locale)