Use official upstream vim filetype

alerque · alerque · commit a2462c650dd1 · 2019-10-03T15:07:36.000+03:00
diff --git a/ftdetect/rmarkdown.vim b/ftdetect/rmarkdown.vim
@@ -1,4 +1,4 @@
 augroup rmarkdown
-    au! BufRead,BufNewFile *.Rmd  set filetype=rmarkdown
-    au! BufRead,BufNewFile *.Rpres  set filetype=rmarkdown
+    au! BufRead,BufNewFile *.Rmd  set filetype=rmd
+    au! BufRead,BufNewFile *.Rpres  set filetype=rmd
 augroup END
