message: fix(config): check if window.screen exists before calculating the dpr.
  enhance ecomfe/zrender#623 and fix apache/incubator-echarts#13940.
diff: @@ -3,7 +3,7 @@ let dpr = 1;
  // If in browser environment
  if (typeof window !== 'undefined') {
  dpr = Math.max(window.devicePixelRatio
  - || ((window.screen as any).deviceXDPI / (window.screen as any).logicalXDPI)
  + || (window.screen && (window.screen as any).deviceXDPI / (window.screen as any).logicalXDPI)
  || 1, 1);
  }
  