Update OrderCancelMsg.java

TESTED this way:

package org.yats.trading;

import org.joda.time.DateTime;
import org.yats.common.UniqueId;
import org.yats.messagebus.messages.OrderCancelMsg;

/**
 * Created by emiliano on 14/05/2014.
 */
public class testEmiliano {

    public static void main (String args[])
    {
        OrderCancel aa = OrderCancel.create().withExternalAccount("1005390").withBookSide(BookSide.BID).withProductId("4663789").withOrderId(UniqueId.createFromString("12345")).withTimestamp(DateTime.now());
        OrderCancel bb = OrderCancel.create().withExternalAccount("1005390").withBookSide(BookSide.BID).withProductId("4663789").withOrderId(UniqueId.createFromString("12345")).withTimestamp(DateTime.now());
        OrderCancelMsg a = OrderCancelMsg.createFromOrderCancel(aa);
        OrderCancelMsg b = OrderCancelMsg.createFromOrderCancel(bb);

        System.out.println(a.isSameAs(b));

    }

}

Returns TRUE! If I don't touch UniqueID and let it be automatically generated, like this:

package org.yats.trading;

import org.joda.time.DateTime;
import org.yats.messagebus.messages.OrderCancelMsg;

/**
 * Created by emiliano on 14/05/2014.
 */
public class testEmiliano {

    public static void main (String args[])
    {
        OrderCancel aa = OrderCancel.create().withExternalAccount("1005390").withBookSide(BookSide.BID).withProductId("4663789").withTimestamp(DateTime.now());
        OrderCancel bb = OrderCancel.create().withExternalAccount("1005390").withBookSide(BookSide.BID).withProductId("4663789").withTimestamp(DateTime.now());
        OrderCancelMsg a = OrderCancelMsg.createFromOrderCancel(aa);
        OrderCancelMsg b = OrderCancelMsg.createFromOrderCancel(bb);

        System.out.println(a.isSameAs(b));

    }

}

Returns false, since the UniqueId is generated, and thus differs in OrderCancelMsg a and b.
Merge pull request #31 from NeoSephiroth/patch-2

Update OrderCancelMsg.java