e_band() now displays correct upper lines

[shrektan]

Closes #237

Code

library(echarts4r)
df <- data.frame(
  x = 1:10,
  y = runif(10, 5, 10)
) %>%
  dplyr::mutate(
    lwr = y - 2,
    upr = y + 2
  )

df %>%
  e_charts(x) %>%
  e_line(y) %>%
  e_band(lwr, upr)

Before the PR

After the PR

[JohnCoene]

Looks good, thank you. Can you add yourself as ctb to the DESCRIPTION (if you want to)?

[shrektan]

Sure, added 😃

[JohnCoene]

Thanks!