TypeError: __init__() got an unexpected keyword argument 'headers'

```
TypeError: __init__() got an unexpected keyword argument 'headers'
```

This is what I get when I run this within a Flask app like this:

```
from flask import Flask
app = Flask(__name__)

from robobrowser import RoboBrowser

@app.route("/")
def hello():

browser = RoboBrowser(headers={'User-Agent': 'a python robot'})
browser.open('http://google.com/')

return 'Hello'

if __name__ == "__main__":
app.run(host="localhost", debug=True)
```

What could be causing this?

I installed RoboBrowser in a virtualenv using pip 7.1.2, python 2.7.10, Windows 10