Slack-compatible notification strategies expect "url" for switch name, should be "-url"

Steps to reproduce:

Configure a notification command in notificationCommands.xml as follows:

Hit it with a notification.

Expected result: Notification sent to channel associated with the webhook specified with the -url switch substitution

Actual result: Notification fails to be sent, with the following appearing in notifd.log:

Workaround: Specify the webhook url using switch url rather than -url (omit the leading dash character)

Update: An equivalent problem exists with the -username, -iconurl, -iconemoji, and -channel switches. These problems can be worked around in the equivalent way as described for -url above.