Double-command fix

[kentcdodds]

When a message is edited, the bot checks whether it contains any commands and re-executes those commands. This is useful for when people update their command (for a typo fix). But it can trigger the bot to run the same thing twice if the thing that was edited is irrelevant extra stuff (like text before the command, or when embedded links are expanded which counts as an edit).

To fix this, we could determine the arguments in the pre-edit message and the post-edit message and if they're the same, do not re-execute the command.