install, don't update
install, don't update

Per [a comment on my blog post](https://mwop.net/blog/2015-12-14-secure-phar-automation.html#comment-2410525639),
`install` is the proper command here, as it ensures the same dependencies are
used as for the tests. (`update` could potentially pull new versions!)

zendframework/zend-component-installer,weierophinney/component-installer,weierophinney/component-installer