You have updated the Lead Mappings field in a Sandbox, and want to now publish these changes into production.
Example
I created a new custom field on both Lead and Account objects labled "LinkedIn Industry". I want to ensure that whenever a lead is converted, if there is a value on the LinkedIn Industry field, it is published to the related Account during lead conversion.
Resolution
Use the metadatatype LeadConvertSettings in your package.xml file:
