Add diff to treesitter's ensure_installed languages (nvim-lua#908)

Author: rmacklin

init.lua

@@ -844,7 +844,7 @@ require('lazy').setup({
     'nvim-treesitter/nvim-treesitter',
     build = ':TSUpdate',
     opts = {
-      ensure_installed = { 'bash', 'c', 'html', 'lua', 'luadoc', 'markdown', 'vim', 'vimdoc' },
+      ensure_installed = { 'bash', 'c', 'diff', 'html', 'lua', 'luadoc', 'markdown', 'vim', 'vimdoc' },
       -- Autoinstall languages that are not installed
       auto_install = true,
       highlight = {