ValueError: invalid literal for int() with base 10 (backend/alpaca.py: `int(pos.qty)` should be `float` ?)

using `context.portfolio.positions` gives
> ValueError: invalid literal for int() with base 10: '418.8667'

from https://github.com/alpacahq/pylivetrader/blob/master/pylivetrader/backend/alpaca.py#L244
```
File "alpaca_short_bsf46.py", line 145, in close_previous_day
for sec in context.portfolio.positions:
File "/usr/local/lib/python3.6/site-packages/pylivetrader/algorithm.py", line 512, in portfolio
self._portfolio = self._backend.portfolio
File "/usr/local/lib/python3.6/site-packages/pylivetrader/backend/alpaca.py", line 268, in portfolio
z_portfolio.positions = self.positions
File "/usr/local/lib/python3.6/site-packages/pylivetrader/backend/alpaca.py", line 244, in positions
z_position.amount = int(pos.qty)
ValueError: invalid literal for int() with base 10: '418.8667'
```

changing `int(pos.qty)` to `float` in `backend/alpaca.py` gets past this error

```
pip show pylivetrader
Name: pylivetrader
Version: 0.7.1
Summary: simple live trading framework
Home-page: https://github.com/alpacahq/pylivetrader.git
```