Fix deprecated create method

• Fix deprecated create method
• Update readme
• Fix unit tests

Fix UnitTests and update composer dependencies

Update composer requirements (#9)

- Use phpunit 8
- Update unit tests
- Only add supported symfony versions to composer.json
- Only add supported php version to travis.yaml

Allow Symfony4

v3.1.3

allow symfony 5 (#8)

v3.1.2

Handle deprecation notice for symfony 4.2 (#6)

v3.1.1

SF4 compatibility, service must be public (#5)

v3.1.0: Symfony4 compatibility (#4)

* Symfony4 compatibility
* Fix UnitTests