prompt: Fix 2 deprecation warnings

An oversaw in a previous commit introduced deprecation warnings
on the default config.

lib/awful/widget/prompt.lua

@@ -20,13 +20,15 @@ local widgetprompt = { mt = {} }
 --
 -- @param promptbox The promptbox to run.
 local function run(promptbox)
-    return prompt.run({ prompt = promptbox.prompt },
-                      promptbox.widget,
-                      function (...)
+    return prompt.run {
+        prompt              = promptbox.prompt,
+        textbox             = promptbox.widget,
+        completion_callback = completion.shell,
+        history_path        = util.get_cache_dir() .. "/history",
+        exe_callback        = function (...)
             promptbox:spawn_and_handle_error(...)
         end,
-                      completion.shell,
-                      util.get_cache_dir() .. "/history")
+    }
 end
 
 local function spawn_and_handle_error(self, ...)

lib/menubar/init.lua

@@ -440,15 +440,17 @@ function menubar.show(scr)
     menulist_update(nil, scr)
 
     local prompt_args = menubar.prompt_args or {}
-    prompt_args.prompt = "Run: "
-    awful.prompt.run(prompt_args, instance.prompt.widget,
-                function() end,            -- exe_callback function set to do nothing
-                awful.completion.shell,     -- completion_callback
-                awful.util.get_cache_dir() .. "/history_menu",
-                nil,
-                menubar.hide, function(query) menulist_update(query, scr) end,
-                prompt_keypressed_callback
-                )
+
+    awful.prompt.run(setmetatable({
+        prompt              = "Run: ",
+        textbox             = instance.prompt.widget,
+        completion_callback = awful.completion.shell,
+        history_path        = awful.util.get_cache_dir() .. "/history_menu",
+        done_callback       = menubar.hide,
+        changed_callback    = function(query) menulist_update(query, scr) end,
+        keypressed_callback = prompt_keypressed_callback
+    }, {__index=prompt_args}))
+
     instance.wibox.visible = true
 end