nvim: Use nvim-lint for linting markdown with vale

This effectively reverts 3ea83c6 and f4ee744.

nvim/.config/nvim/after/ftplugin/markdown.lua

@@ -2,5 +2,7 @@ vim.bo.textwidth = 80
 
 vim.api.nvim_create_autocmd({ "BufWritePost" }, {
   buffer  = 0,
-  command = 'Vale',
+  callback = function()
+    require("lint").try_lint()
+  end,
 })

nvim/.config/nvim/after/plugin/nvim-lint.lua

@@ -10,6 +10,7 @@ nvim_lint.linters_by_ft = {
   haskell    = { 'hlint' },
   javascript = { 'eslint_d' },
   lua        = { 'luacheck' },
+  markdown   = { 'vale' },
   python     = { 'pylint' },
   sh         = { 'shellcheck' },
   typescript = { 'eslint_d' },

nvim/.config/nvim/lua/plugins.lua

@@ -87,7 +87,6 @@ local init = function ()
   }
   use 'andymass/vim-matchup'
   use 'christoomey/vim-tmux-navigator'
-  use 'marcelofern/vale.nvim'
   use {
     "windwp/nvim-autopairs",
     config = function()