Use local notifier package instead of outdated github.com/damicon/zfs…

[Danoontjes]

Use local notifier package instead of outdated github.com/damicon/zfswatcher/notifier.

Recent changes in zfswatcher/notifier were not incorporated when building the package because the notifier package was pulled from github.com/damicon/zfswatcher/notifier. I have changed the files that used the damicon version to point to the local version. I also had to change the Makefile so it would do a 'go mod init zfswatcher' and create a go.mod file. Without that go would not find the notifier package. If there is a better way to do this, feel free to change ;)