Laravel version bug fixed and README updated

`Application::VERSION` constant is [added](https://github.com/laravel/framework/commit/c6d0d43fcc85db47e9a9dac4e5d0f956e032fedb) to BETA4 and beta 4 is not [tagged](https://github.com/laravel/framework/tags) yet. So it must be checked before set.

And i changed  `Region::US_WEST_2` to `Aws\Common\Enum\Region::US_WEST_2` in `app/config/aws.php`.