Fix cache directory upgrading - do not try to remove the destination directory.

src/Composer/Factory.php

@@ -118,10 +118,12 @@ class Factory
                             @rename($child, $dir.'/'.basename($child));
                         }
                     }
+                    if ($config->get('cache-dir') != $oldPath) {
                         @rmdir($oldPath);
                     }
                 }
             }
+        }
 
         return $config;
     }