Add PHP 7.4 and 8.0snapshot for travis CI build

[smoench]

No description provided.

[coveralls]

Coverage remained the same at 94.615% when pulling 416397a on smoench:patch-1 into 1493114 on oradwell:master.

[oradwell]

thanks for this PR. Nice and clean!

[smoench]

@oradwell Currently one test is failing on PHP 8.0 because of:

1) OckCyp\CoversValidator\Tests\Command\ValidateCommandTest::testSkipsEmptyTestClasses
preg_match(): Compilation failed: PCRE2 does not support \F, \L, \l, \N{name}, \U, or \u at offset 9
/home/travis/build/oradwell/covers-validator/tests/BaseTestCase.php:35
/home/travis/build/oradwell/covers-validator/tests/Command/ValidateCommandTest.php:186

Travis integration seems to be broken and the migration to travis-ci.com is needed.

[oradwell]

@smoench I'll sort all out once the tests complete