Only do complex string test with stringi. (#74)

tests/testthat/test-stabilize_chr.R

@@ -34,6 +34,7 @@ test_that("stabilize_chr() checks values", {
 })
 
 test_that("stabilize_chr() works with complex url regex", {
+  skip_if_not_installed("stringi")
   url_regex <- r"(^(?:(?:(?:https?|ftp):)?\/\/)?(?:\S+(?::\S*)?@)?(?:(?!(?:10|127)(?:\.\d{1,3}){3})(?!(?:169\.254|192\.168)(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z0-9\u00a1-\uffff][a-z0-9\u00a1-\uffff_-]{0,62})?[a-z0-9\u00a1-\uffff]\.)+(?:[a-z\u00a1-\uffff]{2,}\.?))(?::\d{2,5})?(?:[/?#]\S*)?$)"
   expect_snapshot(
     stabilize_chr(