Correctly filter items when selecting a state, fixes #81

The `onSelect` logic was setting `state.unitedStates` to an empty array
which gave the impression that there were no matching results when the menu
was reopened.

Author: CMTegner

examples/custom-menu/app.js

@@ -25,7 +25,7 @@ let App = React.createClass({
           inputProps={{name: "US state"}}
           items={this.state.unitedStates}
           getItemValue={(item) => item.name}
-          onSelect={() => this.setState({ unitedStates: [] }) }
+          onSelect={(_, state) => this.setState({ unitedStates: [state] }) }
           onChange={(event, value) => {
             this.setState({loading: true})
             fakeRequest(value, (items) => {