nvim: lsp: fix lua server and enable more completion

.config/nvim/lua/my/lsp.lua

@@ -79,7 +79,7 @@ packer.use {
             }
         end
 
-        if vim.fn.executable('lua-language-server' > 0) then
+        if vim.fn.executable('lua-language-server') > 0 then
             require'lspconfig'.sumneko_lua.setup {
                 settings = {
                     Lua = {
@@ -95,6 +95,10 @@ packer.use {
                         telemetry = {
                             enable = false,
                         },
+                        completion = {
+                            -- complete full function signature
+                            callSnippet = 'Replace',
+                        },
                     },
                 },
                 on_attach = on_attach,