Remove restriction

Hi,

I've been encountering a strange issue today with Zend Http client. I was doing an OAuth authorization call to Stripe API (https://stripe.com/docs/connect/reference#post-token), but had the following error:

Zend\Http\Header\Exception\InvalidArgumentException:
Cookie name cannot contain these characters: =,; \t\r\n\013\014 (session=)

After lot of debugging, it appeared that Stripe sent three cookies: http://cl.ly/image/2E232m072h47

The first one is the problematic one because it uses "=". Removing the check make it works.

Please note that I couldn't find a clear documentation that stated that all those characters were not allowed. Furthermore, I tried the exact same call using another PHP client (Guzzle) and it worked without any issue, so I suppose they do not make this check. Lastly, this feature was not tested at all so I suppose it's safe to remove this check.

(I've tried to check on the Internet if other Stripe users had this problem in other languages, and couldn't find anything)