utils/morty.sh: set morty key to avoid service abuse

- https://github.com/asciimoo/searx/issues/1871#issuecomment-592459798



    make install all

generates random MORTY_KEY, install service with that key and sets option in the
searx settingy.yml file.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>