Point to new location for vfstream repo

README.md

 * [PHPT](https://qa.php.net/write-test.php) - A test tool used by PHP itself.
 * [PHPUnit](https://github.com/sebastianbergmann/phpunit) - A unit testing framework.
 * [Prophecy](https://github.com/phpspec/prophecy) - A highly opinionated mocking framework.
-* [VFS Stream](https://github.com/mikey179/vfsStream) - A virtual filesystem stream wrapper for testing.
+* [VFS Stream](https://github.com/bovigo/vfsStream) - A virtual filesystem stream wrapper for testing.
 
 ### Continuous Integration
 *Libraries and applications for continuous integration.*