Fix visualizer margins

Summary:
Found a bug in the archived device visualizer. I realized I never actually announced this feature to anyone, so fixing it up before doing so.

CHANGELOG: Visual Android View inspection available in layout plugin export files.

Reviewed By: passy

Differential Revision: D22548586

fbshipit-source-id: bcb5b8bee6aac7c76354d2c7cb44d72c7d23f5ca

desktop/app/src/ui/components/elements-inspector/Visualizer.tsx

@@ -19,6 +19,7 @@ export function VisualizerPortal(props: {
   screenshotURL: string;
   screenDimensions: {width: number; height: number};
 }) {
+  props.container.style.margin = '0';
   const element: Element | null | '' =
     props.highlightedElement && props.elements[props.highlightedElement];