Doc - change bootstrap 4 theme status to published

Author: epicfaace

docs/usage/themes.md

@@ -8,7 +8,7 @@ meaning that you must load the Bootstrap stylesheet on the page to view the form
  Theme Name | Status | Package Name / Link
  ---------- | ------- | -----------
  Bootstrap 3 (default) | Published | `@rjsf/core`
- Bootstrap 4 | Draft | `@rjsf/bootstrap-4`
+ Bootstrap 4 | Published | `@rjsf/bootstrap-4`
  material-ui | Published | `@rjsf/material-ui`
  fluent-ui | Published | `@rjsf/fluent-ui`
  antd | Published | `@rjsf/antd`