Use prod environment when using --no-dev

Hi everyone.

I propose this little fix to fix this issue : https://github.com/sensiolabs/SensioDistributionBundle/issues/139

I've got the same problem. I'm using a bundle only in dev environment, but when I execute ```composer install --no-dev``` but the scriptHandler launch a cache:clear in dev environment. It's a problem because the cache:clear is launched in dev environment... but one of the bundle registered in the AppKernel is not installed by composer due to the ```--no-dev```. So I've got a "class not found" during the ```cache:clear```.