Fixing Firefox RSS handling

src/app.js

@@ -160,7 +160,7 @@ module.exports = (config) => {
           });
         lastRSS = feed.xml();
       }
-      res.type('rss').send(lastRSS);
+      res.type(req.headers['user-agent'].match(/Mozilla/) ? 'xml' : 'rss').send(lastRSS);
     } else {
       showError(req.path, 404, res);
     }

test/app.test.js

@@ -175,6 +175,7 @@ describe('Test RSS feed', () => {
   test('200 empty rss', (done) => {
     request(app).get('/rsstest').then((response) => {
       expect(response.statusCode).toBe(200);
+      expect(response.type).toBe('application/rss+xml');
       expect(response.text.length).toBeGreaterThan(0);
       expect(response.text.split('<item>').length).toBe(1);
       done();