Typo in entrypoints

[wcooley]

In setup.py, the pytest11 entrypoint is called pyest_osxnotify -- note the missing "t".

You might also consider naming the entrypoint just "osxnotify". The one place that I know this is used for this plugin is disabling it from the command-line: Currently one has to use -p no:pyest_osxnotify; it would be more conventional to be able to use -p no:osxnotify.