Allow user output option in phpspec.yml to override defaults.

I wanted to put my coverage report into `coverage/php`, but the option didn't get set. 

here is my phpspec.yml:

> extensions:
>     - PhpSpec\Extension\CodeCoverageExtension
> code_coverage:
>     output: coverage/php

basically in setOptions, $this->options & $options were the wrong way around, but rather than swap them I used array_merge.