feat: make default cache directory R version

portable with rappdirs::user_cache_dir()

Author: dshemetov

DESCRIPTION

@@ -35,6 +35,7 @@ Imports:
     MMWRweek,
     purrr,
     openssl,
+    rappdirs,
     readr,
     tibble,
     usethis,

R/cache.R

@@ -76,9 +76,9 @@ cache_environ$epidatr_cache <- NULL
 #' )
 #'
 #' @param cache_dir the directory in which the cache is stored. By default, this
-#'   is `tools::R_user_dir()` if on R 4.0+, but must be specified for earlier
-#'   versions of R. The path can be either relative or absolute. The
-#'   environmental variable is `EPIDATR_CACHE_DIR`.
+#'   is `rappdirs::user_cache_dir("R", version = "epidatr")`. The path can be
+#'   either relative or absolute. The environmental variable is
+#'   `EPIDATR_CACHE_DIR`.
 #' @param days the maximum length of time in days to keep any particular cached
 #'   call. By default this is `1`. The environmental variable is
 #'   `EPIDATR_CACHE_MAX_AGE_DAYS`.
@@ -103,8 +103,8 @@ set_cache <- function(cache_dir = NULL,
                       max_size = NULL,
                       logfile = NULL,
                       confirm = TRUE) {
-  if (is.null(cache_dir) && sessionInfo()$R.version$major >= 4) {
-    cache_dir <- Sys.getenv("EPIDATR_CACHE_DIR", unset = tools::R_user_dir("epidatr"))
+  if (is.null(cache_dir)) {
+    cache_dir <- Sys.getenv("EPIDATR_CACHE_DIR", unset = rappdirs::user_cache_dir("R", version = "epidatr"))
   } else if (is.null(cache_dir)) {
     # earlier version, so no tools
     cache_dir <- Sys.getenv("EPIDATR_CACHE_DIR")