Build test support for PHP 8, and fixes

Update travis config, test php 8 versions, fix php 8/8.1 errors (#13)

* Update travis config, test php 8 versions

* Update the way php is defined, put in place structure to allow testing laravel 9

* Forgot to remove matrix

* Fix up travis config, esp envs global vs jobs

* Just add a comment for future reference

* Fix sorting for php 8

* Use bionic for php 8.1

* After looking at the test, we want the highest limit

* Try 8.1.0 based on suggestions on travisci forums

* Try and cast nulls to string for php 8.1 compact

* Drop 8.1 for now (too many fixes)