建议将lineDy样式的效果修改为平行线

[ageeye-cn]

maptalks's version and what browser you use?

Issue description

目前设置lineDy样式后，当line不是一条水平线时，效果不佳，当line是一条垂线时，则完全没有效果

Please provide a reproduction URL (on any jsfiddle like site)

[fuzhenn]

You need a new symbol lineOffset rather than lineDy