Update readme.txt for consistent default bootstrap version

there was a contradition on lines 74 & 79 as to what is the default bootstrap version.

Author: knesbit-cars

readme.txt

@@ -71,8 +71,8 @@ This plugin supports Bootstrap v4 and v5.
 
 The version can be selected in the plugin settings (Settings > Bootstrap Blocks) or by defining the `WP_BOOTSTRAP_BLOCKS_BOOTSTRAP_VERSION` constant in the `wp-config.php` file:
 
-* Bootstrap 4 (default): `define( 'WP_BOOTSTRAP_BLOCKS_BOOTSTRAP_VERSION', '4' );`
-* Bootstrap 5: `define( 'WP_BOOTSTRAP_BLOCKS_BOOTSTRAP_VERSION', '5' );`
+* Bootstrap 4: `define( 'WP_BOOTSTRAP_BLOCKS_BOOTSTRAP_VERSION', '4' );`
+* Bootstrap 5 (default): `define( 'WP_BOOTSTRAP_BLOCKS_BOOTSTRAP_VERSION', '5' );`
 
 Possible values right now are `'4'` or `'5'`. By default Bootstrap version **5** is selected.