Compatibility with symfony 4

[giuseppenucifora]

Can you help me to upgrade for sf4?

[reyostallenberg]

I would like to upgrade to sf4.3+

Shall I make a PR @helmut-hoffer-von-ankershoffen ? Or did you quit working on it?

[reyostallenberg]

In lack of response I produced a replacement bundle with support for sf4.3+ and a more modern client (HttPlug based), see https://github.com/ConnectHolland/uptime-robot-bundle