Fixed keepalive JSON object

Previous:
```Text
{
    "exabgp": "3.4.0",
    "time": 1405934239,
    "host": "producer.local",
    "pid": "14590",
    "ppid": "14460",
    "counter": 3,
    "type": "keepalive",
    "header": "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF001304",
    "neighbor": {
        "ip": "192.168.33.12",
        
    }
}
```

Now:
```Text
{ "exabgp": "3.4.0", "time": 1405936047, "host" : "producer.local", "pid" : "15171", "ppid" : "14460", "counter": 4, "type": "keepalive", "header": "FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF001304", "neighbor": { "ip:": "192.168.33.12"} }
```