Merge pull request #550 from FormidableLabs/bug/voronoi-tooltip-posit…

…ioning

fix shared tooltip positioning bug

src/components/containers/victory-voronoi-container.js

@@ -202,7 +202,7 @@ export const voronoiContainerMixin = (base) => class VictoryVoronoiContainer ext
       this.getDefaultLabelProps(props, points),
     );
     const labelPosition = this.getLabelPosition(props, points, labelProps);
-    return { ...labelPosition, ...labelProps };
+    return defaults({}, labelPosition, labelProps);
   }
 
   getTooltip(props) {