BUG: Can't sort grants by `deadline_current`

[juanmapf]

Describe the bug
deadline_current is listed as a possible value for ordering (Allowed values are: deadline_current, last_updated, posted_date, rank.) but when sent to the /grants endpoint, the response is:

Cannot resolve keyword 'deadline_current' into field. Choices are: additional_info_link, additional_info_link_description, agency, agency_code, agency_id, applicant_eligibility_description, applicant_types, attachments, award_ceiling, award_floor, cfda_numbers, cost_sharing_required, created, description, estimated_application_response_date, estimated_application_response_date_description, estimated_project_start_date, estimated_synopsis_post_date, estimated_total_funding, expected_number_of_awards, forecast, forecast_version, funding_activity_category_description, funding_category_codes, funding_category_description, funding_instruments, grant_id, grantor_contact_email, grantor_contact_name, grantor_contact_phone, is_archived, last_updated, modified, opportunity_category, opportunity_history, opportunity_number, opportunity_packages, opportunity_status, posted_date, response_date, response_date_description, search_vector, source, synopsis, synopsis_version, title