Add GrumPHP in the third-party integrations

[jubianchi]

We should add phpro/grumphp to third-party integrations.

We should get in touch with the authors (@veewee, @aderuwe) to see if we can use their logo on our website.

Here are some useful links:

• project: https://github.com/phpro/grumphp
• documentation: https://github.com/phpro/grumphp/blob/master/doc/tasks/atoum.md
• twitter: https://twitter.com/GrumPhp

[veewee]

Sounds great! Feel free to use the GrumPHP logo on your website.

[jubianchi]

@veewee thanks!