Add tzdata package in Docker image, to be able to set timezone

[mossroy]

Fixes #100

Tested only on linux/amd64 platform:

$ docker run wait4x:2.8.0-mossroy tcp localhost:8080
2022-10-18T07:46:45Z INF [TCP] Checking the localhost:8080 ...
2022-10-18T07:46:46Z INF [TCP] Checking the localhost:8080 ...
2022-10-18T07:46:47Z INF [TCP] Checking the localhost:8080 ...
^CError: context canceled
$ docker run -e TZ=Europe/Paris wait4x:2.8.0-mossroy tcp localhost:8080
2022-10-18T09:46:51+02:00 INF [TCP] Checking the localhost:8080 ...
2022-10-18T09:46:52+02:00 INF [TCP] Checking the localhost:8080 ...
^C2022-10-18T09:46:53+02:00 INF [TCP] Checking the localhost:8080 ...
Error: context canceled

[atkrad]

@mossroy Thanks for the PR.