patch 8.2.0843: filetype elm not detected

Problem:    Filetype elm not detected.
Solution:   Recognize *.elm files. (closes #6157)

runtime/filetype.vim

@@ -547,6 +547,9 @@ au BufNewFile,BufRead */etc/elinks.conf,*/.elinks/elinks.conf	setf elinks
 " ERicsson LANGuage; Yaws is erlang too
 au BufNewFile,BufRead *.erl,*.hrl,*.yaws	setf erlang
 
+" Elm
+au BufNewFile,BufRead *.elm			setf elm
+
 " Elm Filter Rules file
 au BufNewFile,BufRead filter-rules		setf elmfilt
 

src/testdir/test_filetype.vim

@@ -151,6 +151,7 @@ let s:filename_checks = {
     \ 'ecd': ['file.ecd'],
     \ 'edif': ['file.edf', 'file.edif', 'file.edo'],
     \ 'elinks': ['/etc/elinks.conf', '/.elinks/elinks.conf'],
+    \ 'elm': ['file.elm'],
     \ 'elmfilt': ['filter-rules'],
     \ 'erlang': ['file.erl', 'file.hrl', 'file.yaws'],
     \ 'eruby': ['file.erb', 'file.rhtml'],

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    843,
 /**/
     842,
 /**/