vimPlugins.hardhat-nvim: add overseer-nvim dependency

pkgs/applications/editors/vim/plugins/overrides.nix

···
   };
 
   hardhat-nvim = super.hardhat-nvim.overrideAttrs {
-    dependencies = with self; [ plenary-nvim ];
+    dependencies = with self; [ overseer-nvim plenary-nvim ];
   };
 
   harpoon = super.harpoon.overrideAttrs {