fix wrong destination domain suffix with '.net'

[xNathan]

Issue: pingparsing doesn't handle destination parsing with '.net' domain correctly

Result and steps to appear:

$ pingparsing example.net
{
    "example.net": {
        "destination": "example.ne",
        "packet_transmit": 10,
        "packet_receive": 10,
        "packet_loss_count": 0,
        "packet_loss_rate": 0.0,
        "rtt_min": 189.275,
        "rtt_avg": 266.611,
        "rtt_max": 327.308,
        "rtt_mdev": 42.726,
        "packet_duplicate_count": 0,
        "packet_duplicate_rate": 0.0
    }
}

Expected result:

-        "destination": "example.ne",
+        "destination": "example.net",

The reason is that strip() in Python will remove all characters in function argument.

_parse_destination function tries to remove ping statistics ---, but it removes t in .net, which is not expected.

Add a quick fix for that issue, hope it helps, thanks.

[thombashi]

Thank you for your pull request.