Add support for booleans as values for dcc.RadioItems, dcc.CheckList, and dcc.Dropdown #957

Invalid argument `options[0].value` passed into RadioItems

import dash
import dash_core_components as dcc
import dash_html_components as html

app = dash.Dash(__name__)

app.layout = html.Div([
    dcc.RadioItems(
        options=[
            {'label': 'New York City', 'value': True},
            {'label': 'Montréal', 'value': 'MTL'},
            {'label': 'San Francisco', 'value': 'SF'}
        ],
        value=True
    )
])


if __name__ == '__main__':
    app.run_server(debug=True)