unexpected keyword argument 'locale'

When using the intro code:
```
import humanized_opening_hours as hoh
field = "Mo-Fr 06:00-21:00; Sa,Su 08:00-12:00"
oh = hoh.OHParser(field, locale="en")
```
I get
```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: __init__() got an unexpected keyword argument 'locale'
```