[Feature] Update TravisCI for testing Laravel 5.6

[oanhnn]

In this request:

• Remove .coveralls.yml file (Coveralls will be corrected with TravisCI automatic)
• Add .gitattributes file for line ending (LF) and exclude tests folder when composer require
• Update .gitignore file for ignoring some IDE and OS files
• Update .travis.yml for testing with Laravel 5.5 & 5.6, PHP 7+
• Update composer.json for fix some errors with Laravel 5.6

[coveralls]

Coverage remained the same at 100.0% when pulling e2af1c7 on 4beginner:feature-travis-ci-test-laravel-56 into 9723925 on ohmybrew:master.

[gnikyt]

This is excellent, thank you, I will merge this in!