Use self instead of static in final classes

Merge pull request #7 from ekvedaras/deps-date-time

fix(deps): allow `brick/date-time:~0.8.0`

Merge pull request #5 from brick/orm3

Upgrade to doctrine/orm v3 & doctrine/dbal v4

Compatibility with brick/date-time v0.7

Upgrade Psalm to 5.21.1

Fix tests on lowest dependencies

Looks like php-coveralls does not work properly with Guzzle v6.
Maybe they don't test with their lowest deps?

Prepare for release

Compatibility with brick/date-time 0.5

Lock Psalm version

Merge pull request #2 from enumag/patch-1

Allow doctrine/dbal 3.0