Fix: NOT append to tty

[shka]

Issue: spudlyo/clipetty#20

I noticed that append to tty causes the "Permission denied" as below - It occurred in Termux (not tmux), and the same issue occurred in emacs 26.3 on Termux. Therefore, I changed a parameter in write-region function at the clipetty--emit. I hope that this PR solves your issues also!

$ echo test > `tty`
test
$ echo test >> `tty`
Permission denied

This PR will close spudlyo/clipetty#20 .