x11/xnotify: update to 0.8.1

0.8.1
-add support for specifying time for notification to be alive
-simplify invocation (replace "<... 3<>..." with "0<>...")
-handle SIGUSR1 and SIGUSR2
-minor code changes (rename variables, etc)

0.8.0
-add SEC: (time notification should be visible)

(pin)