Use the correct parameter variables in the hook docs for `wp_upgrade`.

See #27700.

Built from https://develop.svn.wordpress.org/trunk@27998


git-svn-id: http://core.svn.wordpress.org/trunk@27828 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/includes/upgrade.php

@@ -332,8 +332,8 @@ function wp_upgrade() {
 	 *
 	 * @since 3.9.0
 	 *
-	 * @param int $new_db_version The new $wp_db_version.
-	 * @param int $old_db_version The old $wp_db_version.
+	 * @param int $wp_db_version         The new $wp_db_version.
+	 * @param int $wp_current_db_version The old (current) $wp_db_version.
 	 */
 	do_action( 'wp_upgrade', $wp_db_version, $wp_current_db_version );
 }