allows Line shapes to be color by colorScale value

[davelandry]

Line shapes have a static colorAssign function in the default config, which overwrites the colorScale logic that is typically interited by the default shapeConfig.fill in the Viz class.

Removing this one line allows Lines to be colored using colorScale, with one caveat:

If users do not want the sum of all values in a Line to be used, then they must define a custom aggs function.

As an example, here is how you would color something using the max value (cc @AlanORB):

.config({
  aggs: {
    "Growth %": (arr, cb) => Math.max(...arr.map(cb))
  },
  colorScale: "Growth %",
})