etebase_invitation_manager_reject wrongfully invokes accept

[Skycoder42]

Currently, the etebase_invitation_manager_reject method actually invokes this.accept - which is the opposite of what it should do. (See https://github.com/etesync/libetebase/blob/master/src/lib.rs#L2032).

#[no_mangle]
pub unsafe extern fn etebase_invitation_manager_reject(this: &CollectionInvitationManager, invitation: &SignedInvitation) -> i32 {
    try_or_int!(this.accept(invitation)); // should be this.reject(invitation)
    0
}