Docs: Add a @global entry for $wp in redirect_canonical().

Props afzalmultani.
See #41238.

git-svn-id: https://develop.svn.wordpress.org/trunk@41003 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/canonical.php

@@ -32,6 +32,7 @@
  * @global bool $is_IIS
  * @global WP_Query $wp_query
  * @global wpdb $wpdb WordPress database abstraction object.
+ * @global WP $wp Current WordPress environment instance. 
  *
  * @param string $requested_url Optional. The URL that was requested, used to
  *		figure if redirect is needed.