patch 9.0.0604: luacheckrc file is not recognized

Problem:    Luacheckrc file is not recognized.
Solution:   Use lua filetype for luacheckrc. (closes #11236)
diff --git a/runtime/filetype.vim b/runtime/filetype.vim
index 725bb6d..519ea33 100644
--- a/runtime/filetype.vim
+++ b/runtime/filetype.vim
@@ -1112,6 +1112,9 @@
 " Lua
 au BufNewFile,BufRead *.lua			setf lua
 
+" Luacheck
+au BufNewFile,BufRead .luacheckrc		setf lua
+
 " Luarocks
 au BufNewFile,BufRead *.rockspec		setf lua
 
diff --git a/src/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index 1082eeb..8a8ee6c 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -328,7 +328,7 @@
     \ 'lpc': ['file.lpc', 'file.ulpc'],
     \ 'lsl': ['file.lsl'],
     \ 'lss': ['file.lss'],
-    \ 'lua': ['file.lua', 'file.rockspec', 'file.nse'],
+    \ 'lua': ['file.lua', 'file.rockspec', 'file.nse', '.luacheckrc'],
     \ 'lynx': ['lynx.cfg'],
     \ 'lyrics': ['file.lrc'],
     \ 'm3build': ['m3makefile', 'm3overrides'],
diff --git a/src/version.c b/src/version.c
index f6b8827..c96585e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    604,
+/**/
     603,
 /**/
     602,