use the exported xfun::is_rel_path()

Author: yihui

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: bookdown
 Type: Package
 Title: Authoring Books and Technical Documents with R Markdown
-Version: 0.21.3
+Version: 0.21.4
 Authors@R: c(
     person("Yihui", "Xie", role = c("aut", "cre"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666")),
     person("JJ", "Allaire", role = "ctb"),

R/html.R

@@ -1032,7 +1032,7 @@ move_files_html = function(output, lib_dir) {
   f = gsub('[?#].+$', '', f)  # strip the #/? part in links, e.g. a.html#foo
   f = gsub('^[.]/', '', f)  # strip the initial ./, e.g. ./foo.png -> foo.png
   f = f[f != '']
-  f = f[!knitr:::is_abs_path(f)]
+  f = f[xfun::is_rel_path(f)]
   if (getOption('bookdown.js.debug', FALSE)) f = c(f, js_min_sources(f))
   # add leaflet images if any used
   f = c(f, grep('png$', list.files(