Update Cookie.java

[hokiemike84]

Initialized capacity of a StringBuffer to avoid the need for re-sizing. The returned string should be of equal or lesser capacity than the original string.

[stleary]

Hi Mike,
Your recommended change was incorporated during the Java 1.8 update. In the case of Cookie.java, we now have:
StringBuilder sb = new StringBuilder(length);
Thanks for the suggestion,
Sean