Does not run on Travis CI

Hello,

I'd like to know if it is possible to run acceptance tests on Travis CI. By seeing the `.travis.yml` file on the project root directory, I suppose it is possible.

It looks like you are using the deprecated wp-cli installer (https://github.com/wp-cli/wp-cli/wiki/Alternative-Install-Methods#installersh-deprecated), which causes an error. Using the phar file of the wp-cli may be an option.

Apart from it, I'm not sure how it runs on Travis. I'd like to see a working example. Can you update it to make the tests run on Travis? Thank you!

Start with the .travis.yml file in the project root and inspect how the acceptance tests are installed and invoked. Check the deprecated WP-CLI installer mentioned in the issue and evaluate the phar alternative. Done means the acceptance tests run successfully on Travis CI with a working example configuration.

Written by the indexing model from the issue text.