Fix HTTPCookie.secure

[xtyxtyx]

Connection with issue(s)

Resolve issue #118

Testing and Review Notes

According to https://developer.apple.com/documentation/foundation/httpcookiepropertykey/1392985-secure, .secure key of HTTPCookie shouldn't be set when the cookie isn't secure. Otherwise, cookies are always 'secure' and won't work on http urls.

[arnaudelub]

If you want, as the maintainer is out for quite a long time now, we are maintaining this fork:
https://github.com/arnaudelub/flutter_polywebview
package also available on pub.dev:
https://pub.dev/packages/flutter_polywebview

feel free to add you PR on this fork if you want.

[pichillilorenzo]

Released new version 3.0.0. Thanks!