Update CHANGELOG.md

Add 0.4.0 Changelog

Update docs

Update Changelog.

Merge pull request laravel-notification-channels#60 from irazasyed/su…

…pport-php7.1

Add PHP 7.1 Support

Revert

Revise readme to correct class names.

Merge pull request laravel-notification-channels#36 from Lotuashvili/…

…patch-1

Add ability to change button columns

Merge pull request laravel-notification-channels#30 from jackcolley/m…

…aster

Adding support for Laravel 5.6

Merge pull request laravel-notification-channels#21 from okaufmann/ma…

…ster

Allow Laravel version 5.5