magrittr dependency in tests

[crew102]

Perhaps we should come up with a reprex that doesn't require magrittr for this test (so that we can remove a dep on magrittr when running tests):

reprex/tests/testthat/test-undo.R

Lines 145 to 158 in eba1304

	test_that("reprex_invert(venue = 'gh') doesn't strip leading ws", {
	skip_on_cran()
	temporarily()
	input <- c(
	"library(magrittr)",
	"mtcars[, 1:2] %>%",
	" head(n = 1)"
	)
	reprexed <- reprex(
	input = input, venue = "gh", advertise = FALSE, show = FALSE
	)
	inverted <- reprex_invert(reprexed, venue = "gh")
	expect_match(inverted, input[3], all = FALSE, fixed = TRUE)
	})

If you think we to keep the reprex as is (i.e., b/c it provides a realistic example of where leading whitespace would be used), I'd suggest adding skip_if_not_installed("magrittr") to the above test, as well as adding magrittr to Suggests.

Happy to issue a PR for this.