Error after update "ComposerAutoloaderInitd..." (no replies)

Hi,
I have done the last update 2.13.1 and it fell during the automatic update, and now, I get this error message when I try to go on my Piwik page!
Fatal error: Class 'ComposerAutoloaderInitd51538311167b162bd44479d55d6df19' not found in /datas/vol2/w4a144477/var/www/..../htdocs/vendor/autoload.php on line 7

someone have got an idea?