Enable Scrutinizer code coverage analysis

I'm not sure what the normal process is for updating the composer.lock file, so forgive me if doing it in a pull request is presumptive. In hoping to contribute some organization to existing code in the project, I wanted to be able to use a coverage tool so that I can add tests before refactoring. While I can use a local tool, it occurs to me that others may want the same utility and convenience, so I created a feature branch to use Scrutinizer-CI, with Travis-CI uploading coverage reports. 

In order to do this with the parallel test running, I had to use phpcov to merge the separate coverage reports. This required updating phpunit to at least 4.1. I updated the composer.json and composer.lock accordingly, and the Travis builds are succeeding.
this should be an after_script step, not a script step. It is not part of the testing itself.