Run `update` instead of `install` on composer deployments

[romainpoirier]

I am using Gandi Simple Hosting deployment system for Composer.

Each time I deploy (using ssh $GIT_URL 'deploy {repository}.git'), it is running a kind of composer install instead of composer update, which takes a lot of time and is, in most of cases, not the best action to deploy.

How can I set update instead?