message: docs: add nvd3 version badge to readme
diff: @@ -28,6 +28,7 @@ If a third-party plugin becomes really good, we can consider merging into this r
  | Package | Version |
  |--|--|
  | [@superset-ui/legacy-preset-chart-big-number](https://github.com/apache-superset/superset-ui-plugins/tree/master/packages/superset-ui-legacy-preset-chart-big-number) | [![Version](https://img.shields.io/npm/v/@superset-ui/legacy-preset-chart-big-number.svg?style=flat-square)](https://img.shields.io/npm/v/@superset-ui/legacy-preset-chart-big-number.svg?style=flat-square) |
  +| [@superset-ui/legacy-preset-chart-nvd3](https://github.com/apache-superset/superset-ui-plugins/tree/master/packages/superset-ui-legacy-preset-chart-nvd3) | [![Version](https://img.shields.io/npm/v/@superset-ui/legacy-preset-chart-nvd3.svg?style=flat-square)](https://img.shields.io/npm/v/@superset-ui/legacy-preset-chart-nvd3.svg?style=flat-square) |
  | [@superset-ui/legacy-plugin-chart-calendar](https://github.com/apache-superset/superset-ui-plugins/tree/master/packages/superset-ui-legacy-plugin-chart-calendar) | [![Version](https://img.shields.io/npm/v/@superset-ui/legacy-plugin-chart-calendar.svg?style=flat-square)](https://img.shields.io/npm/v/@superset-ui/legacy-plugin-chart-calendar.svg?style=flat-square) |
  | [@superset-ui/legacy-plugin-chart-chord](https://github.com/apache-superset/superset-ui-plugins/tree/master/packages/superset-ui-legacy-plugin-chart-chord) | [![Version](https://img.shields.io/npm/v/@superset-ui/legacy-plugin-chart-chord.svg?style=flat-square)](https://img.shields.io/npm/v/@superset-ui/legacy-plugin-chart-chord.svg?style=flat-square) |
  | [@superset-ui/legacy-plugin-chart-country-map](https://github.com/apache-superset/superset-ui-plugins/tree/master/packages/superset-ui-legacy-plugin-chart-country-map) | [![Version](https://img.shields.io/npm/v/@superset-ui/legacy-plugin-chart-country-map.svg?style=flat-square)](https://img.shields.io/npm/v/@superset-ui/legacy-plugin-chart-country-map.svg?style=flat-square) |
  