bug #206 Fix Symfony3 is now the latest release (ogizanagi)

This PR was merged into the 1.0-dev branch.

Discussion
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Fix Symfony3 is now the latest release

Symfony 3 is now the latest release. 🎉

Fix the following issue:

```bash
symfony new test

 Downloading Symfony...

    4.93 MB/4.93 MB ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓  100%

 Preparing project...

PHP Warning:  require(/Users/Ogi/test/app/SymfonyRequirements.php): failed to open stream: No such file or directory in phar:///usr/local/bin/symfony/src/Symfony/Installer/DownloadCommand.php on line 265

Warning: require(/Users/Ogi/test/app/SymfonyRequirements.php): failed to open stream: No such file or directory in phar:///usr/local/bin/symfony/src/Symfony/Installer/DownloadCommand.php on line 265
PHP Fatal error:  require(): Failed opening required '/Users/Ogi/test/app/SymfonyRequirements.php' (include_path='.:/usr/local/php5/lib/php') in phar:///usr/local/bin/symfony/src/Symfony/Installer/DownloadCommand.php on line 265

Fatal error: require(): Failed opening required '/Users/Ogi/test/app/SymfonyRequirements.php' (include_path='.:/usr/local/php5/lib/php') in phar:///usr/local/bin/symfony/src/Symfony/Installer/DownloadCommand.php on line 265
```

Commits
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1110917 Fix Symfony3 is now the latest release

Author: javiereguiluz

src/Symfony/Installer/DownloadCommand.php

@@ -468,7 +468,7 @@ protected function isEmptyDirectory($dir)
      */
     protected function isSymfony3()
     {
-        return $this->version && '3' === $this->version[0];
+        return '3' === $this->version[0] || 'latest' === $this->version;
     }
 
     private function enableSignalHandler()