use base::isFALSE() instead

yihui/xfun#67

DESCRIPTION

@@ -20,6 +20,7 @@ Description: Use the paged media properties in CSS and the JavaScript
   pages. Each page can have its page size, page numbers, margin boxes, and
   running headers, etc. Applications of this package include books, letters,
   reports, papers, business cards, resumes, and posters.
+Depends: R (>= 3.5.0)
 Imports: rmarkdown (>= 2.13), bookdown (>= 0.8), htmltools, jsonlite, later (>= 1.0.0),
   processx, servr (>= 0.23), httpuv, xfun, websocket
 Suggests: 

NEWS.md

@@ -1,5 +1,6 @@
 # CHANGES IN pagedown VERSION 0.20
 
+- This package requires R >= 3.5.0 now.
 
 # CHANGES IN pagedown VERSION 0.19
 

R/chrome.R

@@ -581,7 +581,7 @@ print_page = function(
         # if a stream handle is received -> callback: command #17 IO.read
         if (is.null(stream_handle <<- msg$result$stream)) {
           writeBin(jsonlite::base64_dec(msg$result$data), output)
-          if (!xfun::isFALSE(outline) && length(toc_infos)) add_outline(output, toc_infos, verbose)
+          if (!isFALSE(outline) && length(toc_infos)) add_outline(output, toc_infos, verbose)
           resolve(output)
           token$done = TRUE
         } else {
@@ -625,7 +625,7 @@ print_page = function(
       },
       {
         # Command #18 received -> callback: add outline & close Chrome
-        if (!xfun::isFALSE(outline) && length(toc_infos)) add_outline(output, toc_infos, verbose)
+        if (!isFALSE(outline) && length(toc_infos)) add_outline(output, toc_infos, verbose)
         resolve(output)
         token$done = TRUE
       }