Corrrected 'other_ref_name' field to 'other_ref_num' on Invoice object

Hello, 

Please pull my changes.  I have a project that depends on populating the field "other_ref_num" on the Invoice object.  I used the changed code, and I was able to successfully populate the field.  I ran the test suite, and the change didn't break any specs.  

If you'd like a reference to the other "otherRefNum" field on the Invoice object, it can be found in this wsdl file here:
https://webservices.netsuite.com/xsd/transactions/v2013_2_0/sales.xsd

Thank you!