Normalise changeEmail check
Normalise changeEmail check

Unlike the checks in `createUser`, `changePassword`, `removeUser`, and
`resetPassword`, the `typeof` check in `changeEmail` seems to be
different.

douglascorrea/angularfire,bpietravalle/angularfire,denisKaranja/angularfire,fbentz/angularfire,bpietravalle/angularfire,FirebaseExtended/angularfire,denisKaranja/angularfire,itxd/angularfire,nbr1ninrsan2/angularfire,bpietravalle/angularfire,itxd/angularfire,nbr1ninrsan2/angularfire,jamestalmage/angularfire,douglascorrea/angularfire,fbentz/angularfire,denisKaranja/angularfire,FirebaseExtended/angularfire,fbentz/angularfire,cesarmarinhorj/angularfire,douglascorrea/angularfire,yoda-yoda/angularfire,yoda-yoda/angularfire,FirebaseExtended/angularfire,cesarmarinhorj/angularfire,cesarmarinhorj/angularfire,jamestalmage/angularfire,jamestalmage/angularfire,itxd/angularfire,nbr1ninrsan2/angularfire,yoda-yoda/angularfire