test: start Nvim with '--headless' #41

Since Nvim 0.3.2 the meaning of --headless was changed to 
more-strictly imply "no UI", and the --embed was changed to
wait until UI attach before continuing startup.

- :help --headless
- :help --embed
- https://github.com/neovim/neovim/wiki/Following-HEAD#20180922
- neovim/neovim#9024

Author: zchee

nvim/nvim_test.go

@@ -26,7 +26,7 @@ import (
 
 func newChildProcess(t *testing.T) (*Nvim, func()) {
 	v, err := NewChildProcess(
-		ChildProcessArgs("-u", "NONE", "-n", "--embed"),
+		ChildProcessArgs("-u", "NONE", "-n", "--embed", "--headless"),
 		ChildProcessEnv([]string{}),
 		ChildProcessLogf(t.Logf))
 	if err != nil {