nu: Add dot-repeat key mapping

We have to manually enable the <a-.> keybinding for nushell, which
emulates the 'insert last token of last command' functionality of e.g.
zsh.

terminal/.config/nushell/config.nu

@@ -51,6 +51,16 @@ $env.config.keybindings = [
             {send: Enter}
         ]
     }
+    {
+        name: insert_last_token
+        modifier: alt
+        keycode: char_.
+        mode: ["emacs", "vi_normal", "vi_insert"]
+        event: [
+          { edit: InsertString, value: "!$" }
+          { send: Enter }
+        ]
+    }
     {
         name: open_editor
         modifier: control