configured persistent undo (#529)

lua/settings.lua

@@ -30,6 +30,9 @@ vim.o.showtabline = 2 -- Always show tabs
 vim.o.showmode = false -- We don't need to see things like -- INSERT -- anymore
 vim.o.backup = false -- This is recommended by coc
 vim.o.writebackup = false -- This is recommended by coc
+vim.o.swapfile = false -- Do not write any swp files
+vim.o.undodir = CACHE_PATH .. '/undo' -- Set undo directory
+vim.o.undofile = true -- Enable persistent undo
 vim.wo.signcolumn = "yes" -- Always show the signcolumn, otherwise it would shift the text each time
 vim.o.updatetime = 300 -- Faster completion
 vim.o.timeoutlen = O.timeoutlen -- By default timeoutlen is 1000 ms