enable spell check for tex docs

vimrc

@@ -67,7 +67,7 @@ set wildignore+=__pycache__
 filetype plugin indent on
 
 set completeopt=longest,menuone
-autocmd FileType gitcommit setlocal spell
+autocmd FileType gitcommit,tex setlocal spell
 autocmd FileType mail setlocal spell spelllang=de_at
 
 " https://github.com/numirias/security/blob/master/doc/2019-06-04_ace-vim-neovim.md#patches