Fix missing `ARGV.next` and incomplete detection of `LaunchDaemon`s

[overhacked]

1. Not sure what change to Homebrew or Ruby caused this issue, but running brew-pkg results in an error when accessing ARGV that Array has no method next. #16 already partially addresses the missing ARGV.next errors, but it missed one. All #16's changes are included in this PR.
2. brew-pkg detects formulae with LaunchDaemons by testing for Formula.plist, but a LaunchDaemon can also be defined by Formula.service. Changed the conditional to check for existence of either. The rest of the LaunchDaemon writing code works as-is.