Fix typo

From Litle_XML_Reference_Guide_XML8.13_V2.24.pdf

4.163 payPalOrderComplete
The payPalOrderComplete element is an optional child of both the capture and sale elements, but is required to close a PayPal order. Set the value to true to close the order, when you have fulfilled the order and do not need to send any further auths or deposits against it. Set the value to false to keep the order open for additional auths or deposits.
configuration: allow specification of an external logger

One can now specify an external logger for XML requests and responses
by setting the logger configuration property:

  LitleOnline::Configuration.logger = Logger.new(STDOUT)

This is mainly useful for the Active Merchant integration.

The default behavior hasn't changed and the printxml config parameter is
still respected.

The implementation could be cleaner by making the logger an instance of
Configuration. This requires though that the LitleXmlMapper.request
signature changes and accepts an instance of Configuration instead of the
hash directly. I didn't implement this since I'm not sure if this API is public
and to avoid making intrusive changes in the test suite.

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
Merge pull request #5 from LessonPlanet/master

Fix typo in LitleOnline::LitleOnlineRequest#sale
Merge pull request #7 from pierre/add-logging-support

configuration: allow specification of an external logger