Use `cookie 0.8.1` to drop reliance on openssl

[w-k-s]

I'm trying to use nickel_cookies 0.2.0 in conjunction with frank_jwt 2.5.1.
frank_jwt 2.5.0 relies on the latest version of openssl v0.9.12.
nickel_cookies 0.2.0 relies on cookie 0.2.5 which relies on openssl 0.7.17.

When I try to build my rust application, I get the following error:

error: native library openssl is being linked to by more than one version of the same package, but it can only be linked once; try updating or pinning your dependencies to ensure that this package only shows up once

The latest version of cookie,0.8.1, has dropped its openssl dependancy. If nickel_cookies updates to the latest version of cookie, this problem would be solved.

[jolhoeft]

I have a fork of this that should fix this issue at https://github.com/jolhoeft/cookies/tree/upgrade

I've been added to the nickel-org team, and should be able to push this fix soon, along with upgrades to nickel.rs itself.