Error Found with AutoNormalize and dataset

- Using this [dataset.csv.zip](https://github.com/FeatureLabs/autonormalize/files/4418093/dataset.csv.zip)

```python
import pandas as pd
import autonormalize as an

data = pd.read_csv('dataset.csv.zip')
es = an.auto_entityset(data,
name="fraud",
index='id',
time_index='datetime')
```
Results in the following error:
```
ValueError: zero-size array to reduction operation maximum which has no identity
```