`plot_map()` warning: "The legacy packages maptools, rgdal, and rgeos, underpinning this package will retire shortly."

[theamarks]

          `plot_map()` warning: "The legacy packages maptools, rgdal, and rgeos, underpinning this package will retire shortly." 

• Update dependencies in plot_map() - "The legacy packages maptools, rgdal, and rgeos, underpinning this package will retire shortly."

Originally posted by @theamarks in #12 (comment)