Returns the path to the local cache as set in the
`R_GOOGLE_CHART_CACHE` environment variable. If that is not set, gets the
system's default cache path for the package as provided by
`tools::R_user_dir()`.
library(package = "gchartsmap")
# set the cache path to a temp foldergchartsmap::gchart_set_cache(path = tempdir())
# check the set cachegchartsmap::gchart_get_cache_path()