Make Travis fails if normalized example is outdated
Make Travis fails if normalized example is outdated

Fix https://github.com/vega/vega-lite/issues/2574

uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite