title: Canvas is not getting created by ReactEcharts
body: <p>i am tying to render a map in a react component using echart Library but it is not showing .
  Below is the simple code for just rendering map without data.</p>
  
  <pre><code>render(){
  
      return(
          &lt;div&gt;
              &lt;ReactEcharts style={{height:410}} 
                option=
                {{
                 geo:{
                      show:true,
                      map:'world'
                      },
  
                 series:[
                        {
                         type:'map',
                         map:'world'
                        }
                        ]
                }}
      &gt;&lt;/ReactEcharts&gt;
          &lt;/div&gt;
      )
  }
  </code></pre>
  
  <p>it should show like this 
  <a href="https://i.stack.imgur.com/Xnac9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Xnac9.png" alt="MAP Preview"></a>
  i have checked the element and found that "Canvas" element is missing from here, i don't know  why it is not getting created for map.(though it is working for other charts like scatter,barchart etc.)</p>
  
  <pre><code>&lt;div class="echarts-for-react " style="height: 410px; -webkit-tap-highlight-color: transparent; user-select: none; position: relative;" _echarts_instance_="ec_1575450559839" size-sensor-id="2"&gt;&lt;div style="position: relative; width: 257px; height: 410px; padding: 0px; margin: 0px; border-width: 0px; cursor: default;"&gt; **CANVAS ELEMENT SHOULD BE CREATED HERE** &lt;/div&gt;&lt;object style="display:block;position:absolute;top:0;left:0;height:100%;width:100%;overflow:hidden;pointer-events:none;z-index:-1;opacity:0" class="size-sensor-object" tabindex="-1" type="text/html" data="about:blank"&gt;&lt;/object&gt;&lt;/div&gt;
  </code></pre>