Laravel Page Speed Versions Save

• Add support for Laravel 9;
• Bump PHP minimun version to ^8.0;

• Drop support for Laravel <6.0;
• Bump PHP minimun version to 7.2.5+;
• Support PHP 8;
• Update dependency constraints in composer.json;
• Recfator all tests:
  • Remove deprecated functions e prepare code to use phpunit 9.0 version;
  • Improvements tests coverage;
• Fix RemoveComments middleware, now it remove JS and CSS comments;
• Fix CollapseWhitespace, now dependent on 'RemoveComments' middleware;
• Update the old phpunit.xml configuration file;
• Update the .travis.yml file and run the tests against in PHP 7.3 / PHP 7.4 / PHP 8;
• Update README.md;

Add support Laravel 8

Fixes remove quotes when attributes contains whitespaces Fixes package keywords typo