Add phpUnit configurationFile option #259
Fixes #229 once mikeerickson/gulp-phpunit#26 is merged.
A recent gulp-phpunit commit gives priority to gulp.src() files for generating the specific command to run. In this case 'config.testing.phpUnit.path + '/*_/_Test.php' was given causing the error to fire as phpunit is looking for an xml file.
While gulp-phpunit has an option to use a file path string set on option.configurationFile, Elixir did not have this option set, and gulp-phpunit would ignore that completely anyway with the priority this way.
With my commit to gulp-phpunit the configurationFile will take priority as long it is set for gulp-phpunit's options..