Bump required R version to R 4.0.0

(Since other tidyverse/r-lib packages will requiring it; this just makes the dependency explicit for covr)

DESCRIPTION

@@ -42,7 +42,7 @@ Description: Track and report code coverage for your package and (optionally)
 URL: https://covr.r-lib.org, https://github.com/r-lib/covr
 BugReports: https://github.com/r-lib/covr/issues
 Depends:
-    R (>= 3.1.0),
+    R (>= 4.0.0),
     methods
 Imports:
     digest,

R/utils.R

@@ -200,10 +200,6 @@ per_line <- function(coverage) {
     class = "line_coverages")
 }
 
-if (getRversion() < "3.2.0") {
-  isNamespaceLoaded <- function(x) x %in% loadedNamespaces()
-}
-
 is_windows <- function() {
   .Platform$OS.type == "windows"
 }

tests/testthat/test-utils.R

@@ -30,18 +30,6 @@ test_that("it works as expected", {
 })
 
 context("get_source_filename")
-test_that("it works", {
-  # R 4.0.0 changes this behavior so `getSrcFilename()` will actually return
-  # "test-utils.R"
-
-  skip_if(getRversion() >= "4.0.0")
-
-  x <- eval(bquote(function() 1))
-
-  expect_identical(getSrcFilename(x), character())
-  expect_identical(get_source_filename(x), "")
-})
-
 test_that("per_line removes blank lines and lines with only punctuation (#387)", {
   skip_on_cran()