use str_replace when tidyverse is imported

Change-Id: Ifda77cfc6d0a38ddb488e04bc95c83f4f89dfec1
diff --git a/demo/recursiveCA.R b/demo/recursiveCA.R
index 1536b7a..e07d4d7 100644
--- a/demo/recursiveCA.R
+++ b/demo/recursiveCA.R
@@ -25,4 +25,4 @@
   cat(file = mdFile, sep = "\n")
 
 rmarkdown::render(mdFile)
-browseURL(gsub("\\.md", ".html", mdFile))
+browseURL(str_replace(mdFile, "\\.md$", ".html"))