travis PHPunit fails

[gregor-j]

PHP versions 7.3 and 7.4 fail with

Code coverage needs to be enabled in php.ini by setting 'xdebug.mode' to 'coverage'

[gregor-j]

Custom ini settings for travis: https://docs.travis-ci.com/user/languages/php/#custom-php-configuration

[gregor-j]

8360ef4 seemed to fix it