set option httpOnly dosen't work 
I was using koa-session.
While I set httpOnly prop like this:

``` javascript
var nickName = encodeURIComponent(userData.data.nick),
        empId = encodeURIComponent(userData.data.empid);
    var cookiesOpt = {
        maxAge : 1296000000,
        path : '/',
        httpOnly: false
    };
    this.cookies.set('nick', nickName, cookiesOpt);
    this.cookies.set('empId', empId, cookiesOpt);
```

I want to get all cookies through document.cookie. but the cookies still have http flag.
Did I miss something? 
