title: Mapbox GL setData to update layer with multiple markers
body: <p>I have a Mapbox GL map with a single layer and multiple markers on that layer, I am trying to update a specific marker, so I am using setData in order to update only one marker but setData will reset the whole layer markers to add only that I am trying to update as the single marker on the whole layer, thus removing all old markers.</p>
  
  <p>By trying to add multiple markers in GEOJson format as an array of GEOJson objects as shown below I get an error:</p>
  
  <pre><code>Uncaught Error: Input data is not a valid GeoJSON object.
  </code></pre>
  
  <p>code:</p>
  
  <pre><code>          map.getSource('cafespots').setData([{
              "type": "Feature",
              "geometry": {
                "type": "Point",
                "coordinates": [31.331849098205566, 30.095422632059062]
              },
              "properties": {
                "marker-symbol": "cafe"
              }
            },{
              "type": "Feature",
              "geometry": {
                "type": "Point",
                "coordinates": [31.39, 30.10]
              },
              "properties": {
                "marker-symbol": "cafe"
              }
            }]);
  </code></pre>
  
  <p>Will appreciate it so much if someone can please help by telling me what I am doing wrong / missing here, thanks</p>