[colorscheme]: remove bg_gutter in Kanagawa plugin.

lua/custom/plugins/kanagawa.lua

@@ -2,7 +2,14 @@ return {
   "rebelot/kanagawa.nvim",
   config = function()
     require("kanagawa").setup {
-      transparent = true
+      transparent = true,
+      colors = {
+        theme = {
+          all = {
+            ui = { bg_gutter = "none" }
+          }
+        }
+      }
     }
     vim.cmd [[colorscheme kanagawa]]
   end,