adjust global composer dependencies
adjust global composer dependencies

 - Explicitly require stable version of composer on self update
 - Explicitly prefer dist packages
 - Remove mockery phpinvoker and the PHP reply boris package
 - Update the required version of PHPUnit to `^7.5` to match cores `composer.json`
saucal/VVV,trepmal/varying-vagrant-vagrants,saucal/VVV,Varying-Vagrant-Vagrants/VVV,Varying-Vagrant-Vagrants/VVV,Varying-Vagrant-Vagrants/VVV,saucal/VVV,trepmal/varying-vagrant-vagrants