Can't import custom icons

Hey guys,
I have made a font set using fontello. used that set already on regular react native project with different approach.
but now with expo when I try to load it, it says “fontFamily “fontello” is not a system font and has not been loaded through Font.loadAsync”

I have followed the docs. and tried even follow other tuts. but none.

this is my code:

import React, {Component} from 'react';
import { View, Text,StyleSheet } from 'react-native';
import { Font, AppLoading } from 'expo';

export default class Icon extends Component {
    state = {
        iconDidLoad: false
    }
    async componentDidMount() {
        await Font.loadAsync({
            fontello: require('../../assets/fonts/fontello.ttf')
        });
        this.setState({iconDidLoad: true});
    }
    render() {
        if (!this.state.iconDidLoad) {
            <AppLoading/>
        }

        return <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
                    <Text style={styles.icon}>{this.props.code}</Text>
                </View>

    }
}

const styles = StyleSheet.create({
    icon: {
        color: 'black',
        fontFamily: 'fontello',
        fontSize: 16
    }
})

what am I missing?
Thanks!