Raising FireError in __init__ is not handled properly

In version 0.3.1 when user attempts to raise error in the `__init__` method the effective error that gets printed is about missing `self` argument. Minimal example:
```
import fire
from fire.core import FireError
class Calc:

def __init__(self):
raise FireError('foo')

def add(self):
pass

if __name__ == "__main__":
fire.Fire(Calc)
```

```
python calc.py add
ERROR: The function received no value for the required argument: self
```

When executed interactively, the error is correct:
```
>>>import calc; import fire
>>>fire.Fire(calc.Calc)
ERROR: foo
```