nixpkgs/neovim: use custom plenary-nvim

https://github.com/NixOS/nixpkgs/pull/178180 caused changes in how
plenary is packaged which is slightly broken.

.config/nixpkgs/neovim/neovim.nix

@@ -10,6 +10,16 @@
 , withPlayground ? false
 }:
 let
+  plenary-nvim = vimUtils.buildVimPluginFrom2Nix {
+    name = "plenary-nvim";
+    src = fetchFromGitHub {
+      owner = "nvim-lua";
+      repo = "plenary.nvim";
+      rev = "986ad71ae930c7d96e812734540511b4ca838aa2";
+      sha256 = "sha256-eBZTFEi7b2CBUakcamhwPcqjzaKg9tAGHNdc4XYUv78=";
+    };
+  };
+
   typescript-nvim = vimUtils.buildVimPluginFrom2Nix {
     name = "typescript-nvim";
     src = fetchFromGitHub {
@@ -64,6 +74,7 @@ neovim.override {
         mini-nvim
         gitsigns-nvim
         sonokai
+        plenary-nvim
 
         (nvim-treesitter.withPlugins (p: with p; [
           tree-sitter-bash