Merge pull request #109 from stloyd/patch-3

[ZipDowloader] Proper exception usage

src/Composer/Downloader/ZipDownloader.php

@@ -22,7 +22,7 @@ class ZipDownloader extends FileDownloader
     protected function extract($file, $path)
     {
         if (!class_exists('ZipArchive')) {
-            throw new \UnexpectedValueException('You need the zip extension enabled to use the ZipDownloader');
+            throw new \RuntimeException('You need the zip extension enabled to use the ZipDownloader');
         }
 
         $zipArchive = new \ZipArchive();