Make sure FileType has called prior to touch syntax

Author: lambdalisue

autoload/fern/internal/viewer.vim

@@ -104,6 +104,7 @@ endfunction
 
 function! s:BufReadCmd() abort
   let helper = fern#helper#new()
+  setlocal filetype=fern
   call helper.fern.renderer.syntax()
   call fern#hook#emit('renderer:syntax', helper)
   let root = helper.sync.get_root_node()