Use new notation for accessing plugin config

Author: unrevised6419

docusaurus/docs/dev-docs/api/plugins/server-api.md

@@ -110,7 +110,7 @@ module.exports = () => ({
 Once defined, the configuration can be accessed:
 
 - with `strapi.plugin('plugin-name').config('some-key')` for a specific configuration property,
-- or with `strapi.config.get('plugin.plugin-name')` for the whole configuration object.
+- or with `strapi.config.get('plugin::plugin-name')` for the whole configuration object.
 
 ## Cron