Updates, Release 2.0.0

[klodoma]

Changes:

• update composer.json dependencies to newer packages
• php >= 7.3 supported, due to dependencies
• fixed Unit-tests

Upon release the linked repository has to be removed from composer.json
(CI is failing if it doesn't exist)

    "repositories": [
        {
            "type": "git",
            "url": "https://github.com/klodoma/portphp-portphp"
        }
    ]

[Seldaek]

You could also update to seld/signal-handler ^1.3, see https://github.com/Seldaek/signal-handler/releases/tag/1.3.0