Bubble property for a Billboard.js chart
Arguments
- bb
- A - billboard- htmlwidgetobject.
- ...
- See https://naver.github.io/billboard.js/release/latest/doc/Options.html#.bubble 
Examples
billboarder() %>% 
  bb_scatterplot(
    data = iris, 
    mapping = bbaes(Sepal.Length, Sepal.Width, group = Species, size = Petal.Width)
  ) %>% 
  bb_bubble(maxR = 10)
billboarder() %>% 
  bb_scatterplot(
    data = iris, 
    mapping = bbaes(Sepal.Length, Sepal.Width, group = Species, size = Petal.Width)
  ) %>% 
  bb_bubble(maxR = JS("function(d) {return Math.sqrt(d.value.z * 20);}"))