Reading duplicated cookies

my bro sends weird cookies (after deleting and installing cookies again):

```
user_id=; session_id=; session_id=XXXXXXX; user_id=6
```

`cookie-parser` parse e.g. `user_id` as a `''`

but expected reading a latest value of each cookie

https://github.com/expressjs/cookie-parser/issues/31
