Set a shared vim undo directory

And be sure to create it during installation

install

@@ -29,6 +29,8 @@ if [[ `uname` == Darwin ]]; then
   stow macos
 fi
 
+mkdir -p ~/.local/share/vim/undo/
+
 cd "$HOME" || exit
 rm -f "${HOME}/.zcompdump*"
 

vim/.vimrc

@@ -46,6 +46,7 @@ set shiftwidth=2
 set smartindent
 set softtabstop=2
 set tabstop=2
+set undodir=~/.local/share/vim/undo/
 set undofile
 
 " Filetype-specific settings