Fix: Configure whitelist filter for coverage generation

[localheinz]

This PR

• configures a whitelist filter for generating code coverage

💁 Without the filter, phpunit complains:

$ vendor/bin/phpunit --coverage-text
PHPUnit 4.8.24 by Sebastian Bergmann and contributors.
Warning:    No whitelist configured for code coverage

...............................................................  63 / 216 ( 29%)
............................................................... 126 / 216 ( 58%)
............................................................... 189 / 216 ( 87%)
...........................

Time: 9.07 seconds, Memory: 26.75Mb

OK (216 tests, 248 assertions)

[localheinz]

@everton-rosario @simonengelhardt

What do you think about using http://codeclimate.com, for example? It's quite useful for tracking coverage, as well as other issues related to the code.

[simonengelhardt]

@localheinz I think that's a great idea. I had considered setting up scrutinizer (since that's used in the main Facebook PHP SDK), but Code Climate seems like an even better option. I'll go ahead and set it up 👍

[localheinz]

@simonengelhardt

Nice!

Maybe this helps: https://github.com/refinery29/php-cs-fixer-config/blob/master/.travis.yml#L37-L42

[everton-rosario]

@simonengelhardt @localheinz
Is this PR going to be used?

[localheinz]

@everton-rosario

I think it only needs to be merged, right?