forkExec leaves zombies

[toke]

Processes spawned by forkExec - via on-click or on-click-right leaves zombie processes.

To reproduce.

   "custom/demo": {
        "format": "Zombienator{}",
        "exec": "date",
        "return-type": "newline",
        "on-click": "touch /tmp/zombietest",
        "on-click-right": "rm /tmp/zombietest"
    }

After clicking on the "Zombienator" defunct processes are visible in the process list.

[toke]

Probably a similar issue is happening with the other open method.
Maybe this open method issue should be handled in a way that #358 is fixed too.
So it is related but not the same.

[Alexays]

Fixed in #370