feat(neovim): Add rainbow-delimiters.nvim

Rainbow parentheses were traditionally buggy with the plugins I used but
nowadays there are newer plugins available that use more flexible
technologies like treesitter.

See: https://github.com/hiphish/rainbow-delimiters.nvim

home/neovim.nix

@@ -641,6 +641,7 @@ in
       emmet-vim
       tagbar
       yats-vim
+      rainbow-delimiters-nvim
     ];
   };