Updated things, following TJ Devries advent of Neovim.

after/ftplugin/gdscript.lua

@@ -0,0 +1,14 @@
+local port = os.getenv('GDScript_Port') or '6005'
+local cmd = vim.lsp.rpc.connect('127.0.0.1', port)
+local pipe = '/tmp/godot.pipe' 
+
+vim.lsp.start({
+  name = 'Godot',
+  cmd = cmd,
+  root_dir = vim.fs.dirname(vim.fs.find({ 'project.godot', '.git' }, { upward = true })[1]),
+  on_attach = function(client, bufnr)
+    vim.api.nvim_command('echo serverstart("' .. pipe .. '")')
+  end
+})
+
+

after/ftplugin/lua.lua

@@ -0,0 +1,3 @@
+local set = vim.opt_local
+
+set.shiftwidth = 2