Retrieve the absolute path when using xml reporter

I understand that the regexp was made in order to retrieve just the name of the file. It could be useful for a quick look at the xml having files without repeated names. But the real utility for the reports is to be imported in tools like Jenkins, and those tools need the absolute path of the file in order to print the source code with the linting errors.

Other approach could be adding an option to the task, something like... `path: 'absolute'` (or 'relative', or 'none'). But I think that most of the times it will be absolute.

I've also modified the tests in order to pass them as we don't know the absolute path of every user.