Fix OptionType constructor.

In my testing, the XML response has the name and value as attributes, not child nodes:

[...]
<PaymentItem xmlns="urn:ebay:apis:eBLBaseComponents" xsi:type="ebl:PaymentItemType">
[...]
  <Options xmlns="urn:ebay:apis:eBLBaseComponents" xsi:type="ebl:OptionType" value="2" name="Adult tickets"></Options>
  <Options xmlns="urn:ebay:apis:eBLBaseComponents" xsi:type="ebl:OptionType" value="2" name="Child tickets"></Options>
</PaymentItem>