format correlations with nsmall = number.digits

[the-mad-statter]

Addresses Issue #275.

The correlation between drat and gear is now listed as 0.70 and not 0.7.

library(dplyr)
library(corrplot)

M <- mtcars |> select(gear, am, drat) |> cor()

corrplot(
  M, 
  type = "lower", 
  diag = FALSE, 
  addCoef.col = "black", 
  number.digits = 2
)

^{Created on 2024-04-29 with reprex v2.1.0}