Changed tenantId to be a Long instead of Integer.

No idea if this is a useful contribution, but easy enough to do so I thought I'd suggest it:

Updated so that `tenantId` is a `Long` rather than an `Integer`.  This is in line with the GORM standard, and makes things work better

    def m = MyDomainClass.build()
    TenantClass.withTenantId(m.id.toInteger()) { ... } // toInteger, or 'as Integer', currently required