plot() throws ggplot2 deprecation warnings

[adcascone]

Hello,

The plot() function in SuperLearner version 2.0.29 throws the following ggplot2 deprecation warnings:

`aes_string()` was deprecated in ggplot2 3.0.0.
ℹ Please use tidy evaluation idioms with `aes()`.
ℹ See also `vignette("ggplot2-in-packages")` for more information.
ℹ The deprecated feature was likely used in the SuperLearner package.
  Please report the issue to the authors.
Backtrace:
    ▆
 1. ├─base::plot(cv_sl) at SuperLearner.R:261:3
 2. └─SuperLearner::plot.CV.SuperLearner(cv_sl)
 3.   ├─ggplot2::ggplot(...)
 4.   ├─ggplot2:::ggplot.default(...)
 5.   │ └─ggplot2:::validate_mapping(mapping)
 6.   │   └─S7::S7_inherits(mapping)
 7.   └─ggplot2::aes_string(x = "X", y = "Y", ymin = "Lower", ymax = "Upper")
 8.     └─ggplot2:::deprecate_warn0(...)

Thank you,
Arianna C.