fix composer.phar not finding the composer.json file

setup/owncloud.sh

@@ -40,6 +40,6 @@ fi
 
 # Currently the mail app dosnt ship with the dependencies, so we need to install them
 curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/lib/owncloud/apps/mail
-php /usr/local/lib/owncloud/apps/mail/composer.phar install
+php /usr/local/lib/owncloud/apps/mail/composer.phar install --working-dir=/usr/local/lib/owncloud/apps/mail
 
 # TODO: enable mail app in ownCloud config?