Fixed the potential ugly prompt which is poor UX (#1091)

Toggleterm's winblend option leads to ugly prompt for some users

https://github.com/akinsho/nvim-toggleterm.lua/issues/70

lua/core/terminal.lua

@@ -26,7 +26,7 @@ M.config = function()
       border = "curved",
       -- width = <value>,
       -- height = <value>,
-      winblend = 3,
+      winblend = 0,
       highlights = {
         border = "Normal",
         background = "Normal",