test: fix overwrite Content-Type (#378)

Author: dmohns

test/tests/server.js

@@ -262,18 +262,21 @@ describe('Server', () => {
   describe('custom Content-Type', () => {
     before((done) => {
       app = express();
+      app.use((req, res, next) => {
+        res.set('Content-Type', 'application/octet-stream');
+        next();
+      });
       const compiler = webpack(webpackConfig);
       instance = middleware(compiler, {
         stats: 'errors-only',
-        logLevel,
-        headers: { 'Content-Type': 'application/octet-stream' }
+        logLevel
       });
       app.use(instance);
       listen = listenShorthand(done);
     });
     after(close);
 
-    it('Do not guess mime type if Content-Type header is found ', (done) => {
+    it('Do not guess mime type if Content-Type header is found', (done) => {
       request(app).get('/bundle.js')
         .expect('Content-Type', 'application/octet-stream')
         .expect(200, done);