request.cookie() expects a string while tough-cookie.Cookie() expects an object.

`request.cookie()` which constructs a new instance of a tough-cookie `Cookie()`
expects a string as a parameter and throws an error if something else is
passed.

However the constructor of `Cookie()` expects, if anything at all, an object for
configuration, see:
https://github.com/goinstant/node-cookie/blob/v0.9.15/lib/cookie.js#L530-L537

This patch removes the parameter check inside `request.cookie()` and just passes
on the optional options object to the `Cookie()` constructor.