fix: remove vim from std for older luacheck compatibility

.luacheckrc

@@ -1,20 +1,16 @@
--- Neovim globals and std
-std = "lua51+vim"
+-- luacheck config for Neovim
+std = "lua51"
 
--- Globals provided by Neovim
-read_globals = {
+globals = {
   "vim",
 }
 
--- Ignore max line length warnings
 ignore = {
-  "631", -- max_line_length
+  "631",
 }
 
--- Don't report unused self arguments in methods
 self = false
 
--- Exclude third-party code
 exclude_files = {
   "lua/custom/plugins/lazy.lua",
 }