Correct VIM patch number in which newrw#BrowseX changed

Author: alerque

ftplugin/markdown.vim

@@ -744,7 +744,7 @@ if !exists('*s:EditUrlUnderCursor')
 endif
 
 function! s:VersionAwareNetrwBrowseX(url)
- if has('patch-9.1.1868')
+ if has('patch-9.1.1588')
  call netrw#BrowseX(a:url)
  elseif has('patch-7.4.567')
  call netrw#BrowseX(a:url, 0)