Schedule a redraw of tabline when setting tabline (#520)

* Schedule a redraw of tabline when setting tabline

The tabline isn't drawn until scrolling the window or opening another file. Opening multiple files at once (e.g. nvim a.txt b.txt) will only show the first.

By performing a deferred redraw of the tabline this fixes this startup behaviour problem.

* Changed to use vim.schedule

lua/lualine.lua

@@ -258,6 +258,9 @@ local function set_tabline()
   if next(config.tabline) ~= nil then
     vim.go.tabline = "%{%v:lua.require'lualine'.tabline()%}"
     vim.go.showtabline = 2
+    vim.schedule(function()
+      vim.api.nvim_command('redrawtabline')
+    end)
   end
 end