Fix php.net redirects

README.md

 * [Why Objects (Usually) Use Less Memory Than Arrays](https://gist.github.com/nikic/5015323) - An article about object and array internals.
 * [PHP Evaluation Order](https://gist.github.com/nikic/6699370) - An article about evaluation order in PHP.
 * PHP Source Code for Developers: [1](http://blog.ircmaxell.com/2012/03/phps-source-code-for-php-developers.html) [2](http://nikic.github.io/2012/03/16/Understanding-PHPs-internal-function-definitions.html) [3](http://blog.ircmaxell.com/2012/03/phps-source-code-for-php-developers_21.html) [4](http://nikic.github.io/2012/03/28/Understanding-PHPs-internal-array-implementation.html) - A series about the PHP source code.
-* Collecting Garbage: [1](http://www.php.net/manual/en/features.gc.refcounting-basics.php) [2](http://www.php.net/manual/en/features.gc.collecting-cycles.php) [3](http://www.php.net/manual/en/features.gc.performance-considerations.php) - A series about the PHP garbage collection internals.
+* Collecting Garbage: [1](http://php.net/manual/en/features.gc.refcounting-basics.php) [2](http://php.net/manual/en/features.gc.collecting-cycles.php) [3](http://php.net/manual/en/features.gc.performance-considerations.php) - A series about the PHP garbage collection internals.
 
 ## PHP Magazines
 *Fantastic PHP-related magazines.*