Fix Xcode 12.5 warnings
Fix Xcode 12.5 warnings

Fixes this warning:
> Using 'class' keyword for protocol inheritance is deprecated; use 'AnyObject' instead
mixpanel/mixpanel-swift,mixpanel/mixpanel-swift,mixpanel/mixpanel-swift,mixpanel/mixpanel-swift,mixpanel/mixpanel-swift