patch 8.2.3686: filetype detection often mixes up Forth and F#

Problem:    Filetype detection often mixes up Forth and F#.
Solution:   Add a function to inspect the file contents. (Doug Kearns)
diff --git a/runtime/scripts.vim b/runtime/scripts.vim
index 0ff8e49..3790b1c 100644
--- a/runtime/scripts.vim
+++ b/runtime/scripts.vim
@@ -198,6 +198,10 @@
   elseif s:name =~# 'fish\>'
     set ft=fish
 
+    " Gforth
+  elseif s:name =~# 'gforth\>'
+    set ft=forth
+
   endif
   unlet s:name