Use "getInitialWorkingDirectory" instead of "getWorkingDirectory"

Follow-up 8d24b61bef4839104db7f05c23400e598a8915e4

src/Composer/Command/ExecCommand.php

@@ -99,7 +99,7 @@ EOT
             try {
                 chdir($this->getApplication()->getInitialWorkingDirectory());
             } catch (\Exception $e) {
-                throw new \RuntimeException('Could not switch back to working directory "'.$this->getApplication()->getWorkingDirectory().'"', 0, $e);
+                throw new \RuntimeException('Could not switch back to working directory "'.$this->getApplication()->getInitialWorkingDirectory().'"', 0, $e);
             }
         }