Update .travis.yml to include recent PHP versions

[sanmai]

Also remove HHVM: it is not going to be PHP-compatible going forward.

[coveralls]

Coverage remained the same at ?% when pulling c8d286d on sanmai:patch-2 into c620f44 on hoaproject:master.

[coveralls]

Coverage remained the same at ?% when pulling 6af2e13 on sanmai:patch-2 into c620f44 on hoaproject:master.

[ohader]

Addressed in PR #114 - unfortunately there's much more to do in order to get complete support for PHP 7.4

• fix/release hoa/test being compatible with PHP 7.4
• adjust hoa/console to call php-cs-fixer with --allow-risky CLI argument
• basically fix & bump all hoa packages for PHP 7.4 compat & switch to new versioning schema (e.g. all packages sharing same major/minor version)

Anyway, I think this PR can be closed → #114

[sanmai]

Sure, about time.