nixpkgs/neovim: add vim-rhubarb for :GBrowse

.config/nixpkgs/neovim/neovim.nix

@@ -42,6 +42,7 @@ neovim.override {
         vim-sensible
         vim-sleuth
         vim-fugitive
+        vim-rhubarb
         vim-surround
         vim-abolish
         undotree