Capture output of the rm command

src/Composer/Util/Filesystem.php

@@ -66,7 +66,7 @@ class Filesystem
             $cmd = sprintf('rm -rf %s', escapeshellarg($directory));
         }
 
-        $result = $this->getProcess()->execute($cmd) === 0;
+        $result = $this->getProcess()->execute($cmd, $output) === 0;
 
         // clear stat cache because external processes aren't tracked by the php stat cache
         clearstatcache();