fix: Install iputils-ping

[Vasniktel]

What does this do / why do we need it?

This PR install iputils-ping package. Without it, protonvpn status produces the following error:

Traceback (most recent call last):
  File "/usr/local/bin/protonvpn", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.8/dist-packages/protonvpn_cli/cli.py", line 73, in main
    cli()
  File "/usr/local/lib/python3.8/dist-packages/protonvpn_cli/cli.py", line 139, in cli
    connection.status()
  File "/usr/local/lib/python3.8/dist-packages/protonvpn_cli/connection.py", line 385, in status
    ping = subprocess.run(["ping", "-c", "1", dns_server],
  File "/usr/lib/python3.8/subprocess.py", line 493, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/usr/lib/python3.8/subprocess.py", line 858, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/lib/python3.8/subprocess.py", line 1704, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'ping'

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