nvim: after/plugin/nvim-lint: Enable linting for Dockerfile

nvim/.config/nvim/after/ftplugin/dockerfile.vim

@@ -0,0 +1 @@
+autocmd! BufWritePost <buffer> lua require('lint').try_lint()

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

@@ -3,6 +3,7 @@ local nvim_lint = require 'lint'
 vim.api.nvim_set_keymap('n', '<LocalLeader>l', ':lua require(\'lint\').try_lint()<CR>', { noremap = true, unique = true })
 
 nvim_lint.linters_by_ft = {
+  dockerfile = { 'hadolint' },
   haskell    = { 'hlint' },
   javascript = { 'eslint' },
   lua        = { 'luacheck' },