add linters, enable plugins

lua/kickstart/plugins/lint.lua

@@ -7,6 +7,10 @@ return {
       local lint = require 'lint'
       lint.linters_by_ft = {
         markdown = { 'markdownlint' },
+        ruby = { 'rubocop' },
+        terraform = { 'tlint' },
+        json = { 'jsonlint' },
+        javascript = { 'eslint_d' },
       }
 
       -- To allow other plugins to add linters to require('lint').linters_by_ft,