Fix hub['count'] error when json output is integer

[lucastobey]

MTR changed their json library sometime after v.92 and it creates the hub['count'] field as an integer instead of a string which breaks this script. Added a line to explicitly convert this value into a string to work with all versions of mtr.

Output in mtr v.92:

   "hubs": [{
      "count": "1",
      "host": "172.17.0.1",
      "Loss%": 0.00,
      "Snt": 10,
      "Last": 0.06,
      "Avg": 0.12,
      "Best": 0.06,
      "Wrst": 0.15,
      "StDev": 0.03
    },

Output in mtr v.95:

 "hubs": [
            {
                "count": 1,
                "host": "_gateway",
                "Loss%": 40.0,
                "Snt": 10,
                "Last": 0.296,
                "Avg": 0.288,
                "Best": 0.261,
                "Wrst": 0.3,
                "StDev": 0.014
            },