This commit fixes a problem in the script that configures the
environment to run the unit tests in the Travis build jobs. The script
was not running `composer install` in the WooCommerce directory, leaving
it installation incomplete and thus the tests were failing.
To fix this problem, this commit adds a call to `composer install` right
after WooCommerce is downloaded in the setup script
(`unit-tests/bin/install.sh`).
Rodrigo Primo
Mike Jolley