Added support for STI on Notifications
Added support for STI on Notifications

This is the same problem found at https://github.com/ging/mailboxer/issues/99, so the fix is really simple.

Just added a base_class when retrieving the recipient class.
sai43/mailboxer,shekibobo/mailboxer,chepri/mailboxer,mailboxer/mailboxer,Design-Collective/mailboxer,roomaroom/mailboxer,noafroboy/mailboxer,jason-wang-0401/mailboxer,netbrick/mailboxer,modsaid/mailboxer,cantonyselim/mailboxer,roomaroom/mailboxer,jason-wang-0401/mailboxer,Groovej/mailboxer,Design-Collective/mailboxer,untitledstartup/mailboxer,noafroboy/mailboxer,jarkadlec/mailboxer,div/mailboxer,netbrick/mailboxer,mailboxer/mailboxer,sai43/mailboxer,mattherick/mailboxer,t27duck/mailboxer,Groovej/mailboxer,lacco/mailboxer,lacco/mailboxer,untitledstartup/mailboxer,chepri/mailboxer,jarkadlec/mailboxer,afalone/mailboxer,mattherick/mailboxer,WeConnect/mailboxer,modsaid/mailboxer,joshtate04/mailboxer,shekibobo/mailboxer,joshtate04/mailboxer,techstars/mailboxer,cantonyselim/mailboxer,t27duck/mailboxer