salesforcedx-templates/lib/templates/project/sfdx-project.json

{
  "packageDirectories": [
    {
      "path": "<%= defaultpackagedir %>",
      "default": true
    }
  ],
  "namespace": "<%= namespace %>",
  "sfdcLoginUrl": "<%= loginurl %>",
  "sourceApiVersion": "<%= apiversion %>"
}