title: Doesn't show markers get from server
body: <p>Sorry for asking similar questions but not to change the original question is advised. So I make another question on slightly different problem. This time I cannot print markers on ComponentDidMount though everyting seems normal. No errors or warnings but markers cannot printed on the map.</p>
  
  <pre><code>import React, { Component } from 'react'
  import { Text, View, StyleSheet, Switch, Alert,TouchableOpacity, AppRegistry} from 'react-native'
  
  import MapView, {Marker, ProviderPropType} from 'react-native-maps';
  import axios from 'axios';
  
  const styles = StyleSheet.create({
    container: {
      ...StyleSheet.absoluteFillObject,
      height: 400,
      width: 400,
      justifyContent: 'flex-end',
      alignItems: 'center',
    },
    map: {
      ...StyleSheet.absoluteFillObject,
    },
  });
  class Fetchdata extends Component {
    constructor (props) {
      super(props);
    };
    state = {
      latitude: 40.35,
      longitude: 27.95,
      markers: []
    };
    componentDidMount = () =&gt; {
      navigator.geolocation.getCurrentPosition(
          (position) =&gt; {
            this.setState({
              latitude: position.coords.latitude,
              longitude: position.coords.longitude,
              error: null,
        });
      },
        (error) =&gt; this.setState({ error: error.message }),
        { enableHighAccuracy: true, timeout: 20000, maximumAge: 1000 },
      );
  
      axios.get('http://isg.info.tr/query_maps.php' + '?latitude=' + this.latitude + '&amp;longitude=' + this.longitude)
      .then(response =&gt; this.setState(response))
     }
     render() {
        return (
          &lt;View style={styles.container}&gt;
            &lt;MapView
                  style={styles.map}
                  initialRegion={{
                  latitude: this.state.latitude,
                  longitude: this.state.longitude,
                  latitudeDelta: 0.015,
                  longitudeDelta: 0.015,
              }}
              &gt;
              {this.state.markers.map((marker, index) =&gt; (
                &lt;MapView.Marker key={marker.index} coordinate={marker.latlng} title={'marker.title'} /&gt;
              ))}
            &lt;/MapView&gt;
        &lt;/View&gt;
        );
     }
  }
  Fetchdata.propTypes = {
    provider: ProviderPropType,
  };
  export default Fetchdata;
  </code></pre>
  
  <p>The JSON file returning</p>
  
  <pre><code>[{
      "markers": {
          "index": "1",
          "latlng": {
              "latitude": "40.3565",
              "longitude": "27.9774"
          }
      }
  }, {
      "markers": {
          "index": "3",
          "latlng": {
              "latitude": "40.3471",
              "longitude": "27.9598"
          }
      }
  }, {
      "markers": {
          "index": "2",
          "latlng": {
              "latitude": "40",
              "longitude": "27.9708"
          }
      }
  }]
  </code></pre>