docs: fix form test example in README (#166)

Author: barraponto

README.md

@@ -87,9 +87,12 @@ chai.request(app)
 // Send some Form Data
 chai.request(app)
   .post('/user/me')
-  .field('_method', 'put')
-  .field('password', '123')
-  .field('confirmPassword', '123')
+  .type('form')
+  .send({
+    '_method': 'put',
+    'password': '123',
+    'confirmPassword': '123'
+  })
 ```
 
 ```js