"IndexError: list index out of range" with piko 7.0

```
File "..../lib/python3.6/site-packages/pikopy/piko.py", line 185, in get_l3_power
    return int(self._get_raw_content()[14])
IndexError: list index out of range
```

The problem seams to be my piko 7.0 only have String 1 and String 2 and no Sting 3. So the positions of L3 values are in lower index values.
