vim: Wrap autocmds in augroups

To prevent the piling up of autocommands when reloading the vimrc, wrap
all autocommands in groups.

.config/vim/vimrc.d/40-keys.vim

@@ -52,7 +52,10 @@ map <leader>st :set spell=!&spell<CR>
 map <leader>sc :call CycleSpellLang()<CR>
 map <leader>ss :set spelllang=
 " Umlaute and sz in Insert and Command-line mode when spelllang is set to `de`
-autocmd OptionSet spelllang silent call NewSpellLang(v:option_new, v:option_old)
+augroup spelllang_set
+	au!
+	autocmd OptionSet spelllang silent call NewSpellLang(v:option_new, v:option_old)
+augroup end
 function! NewSpellLang(new_lang, old_lang)
 	let &spellfile = $XDG_DATA_HOME . '/vim/spell/' . a:new_lang . '.utf-8.add'