Missing cookie values in iOS 10 or lower

[kheldiente]

Hi,
First of all, thank you for making this library. I'm currently migrating a project to WKWebView and this solved my issue of retaining the login session when opening another WKWebView. However, I encountered a bug where some cookie values were missing in iOS 10 or lower.

Usecase:

• When client has logged in, check the session key from cookies and store it locally.
• Check session key and preload it every time the app is opened.

In my case, I need to have a record of all the cookies retrieved by WKCookieWebView and get the session key from there.

I managed to solve this and I would like to file a PR.