is there a way to disable the "goBack" function in react-navigation? basically i have a page (example page A) where people do the login, and then this page go to another page (example page B). i want to disable the goBack from page B to page A.

```
export default class ChatDisponibili extends Component {
  static navigationOptions = {
    title: "CHAT DISPONIBILI",
    headerStyle: {
      backgroundColor: '#3498db',
    },
    headerTintColor: '#fff',
    headerTitleStyle: {
      fontWeight: 'bold',
    }
  };

  ........................

  render() {
    return (
      <View style={styles.container}>
        <ScrollView>
          <FlatList
            data={this.state.data}
            keyExtractor={(item, index) => index.toString()}
            renderItem={this._renderItem}
          />
        </ScrollView>
        <View style={styles.footer}>
          <Text style={styles.footerTesto}>FOOTER DA CAMBIARE</Text>
        </View>
      </View>
    );
  }
}

```