update documentation

Correct the default `site_title:` to `site_name:`

Author: toomanybrians

docs/configuration.md

@@ -502,15 +502,15 @@ This option allows you to override the default MkDocs site title for the title t
 This is useful if you have multiple instances of this plugin for multiple feeds. (For example, one feed
 for the blog, and a second for documentation updates.)
 
-This setting is optional. If you do not include it, the default site title will be used.
+This setting is optional. If you do not include it, the default site name will be used.
 
 ```yaml
 plugins:
   - rss:
       title: My awesome blog feed
 ```
 
-Default: Use the default MkDocs `site_title:`.
+Default: Use the default MkDocs `site_name:`.
 
 ----