switch LOAD_POWER to float

[YuriyKishchenko]

Latest Xiaomi firmware is returning LOAD_POWER as float:
{"cmd":"read_ack","model":"plug","sid":"xxxxx","short_id":xxxx,"data":"{\"voltage\":3600,\"status\":\"off\",\"inuse\":\"0\",\"power_consumed\":\"809\",\"load_power\":\"0.00\"}"}

This is causing startup error:

Jul 21 11:09:24 xxx scl: self.parse_data(device['data'])
Jul 21 11:09:24 xxx scl: File "/home/homeassistant/.homeassistant/custom_components/switch/xiaomi.py", line 96, in parse_data
Jul 21 11:09:24 xxx scl: self._load_power = int(data[LOAD_POWER])
Jul 21 11:09:24 xxx scl: ValueError: invalid literal for int() with base 10: '0.00'#033[0m