Fix the `wp_count_attachments()` PHPDoc to reflect that it returns an object, not array.

See #25412.

Built from https://develop.svn.wordpress.org/trunk@27807


git-svn-id: http://core.svn.wordpress.org/trunk@27641 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/post.php

@@ -2161,7 +2161,7 @@ function wp_count_posts( $type = 'post', $perm = '' ) {
  * @since 2.5.0
  *
  * @param string|array $mime_type Optional. Array or comma-separated list of MIME patterns.
- * @return array Number of posts for each mime type.
+ * @return object An object containing the attachment counts by mime type.
  */
 function wp_count_attachments( $mime_type = '' ) {
 	global $wpdb;