[refine] replace `charts.LegendOpts{Data: []string{}},` to `Show` in Legend. (#104)
[refine] replace `charts.LegendOpts{Data: []string{}},` to `Show` in Legend. (#104)

* [feat] add more options of Legend.

* [refine] replace `charts.LegendOpts{Data: []string{}},` to `Show`.
go-echarts/go-echarts,go-echarts/go-echarts