already have 'doi' key, easier than 'identifiers' for our use case

Author: jspaaks

{{cookiecutter.project_name}}/CITATION.cff

@@ -11,7 +11,6 @@ date-released: 20??-MM-DD
 doi: <insert your DOI here>
 version: "{{ cookiecutter.version }}"
 repository-code: "{{ cookiecutter.repository }}"
-identifiers:
 keywords:
 message: "If you use this software, please cite it using these metadata."
 license: "{{ cookiecutter.license }}"