06/06_lifetimes: Hiding a lifetime that's elided elsewhere is confusing

[iurii-kyrylenko]

Got compiler warning about hiding elided lifetime at line 34:

100-exercises-to-learn-rust/exercises/06_ticket_management/06_lifetimes/src/lib.rs

Lines 34 to 37 in d347d1f

	pub fn iter(&self) -> std::slice::Iter<Ticket> {
	self.tickets.iter()
	}
	}

Suggested fix:

    pub fn iter(&self) -> std::slice::Iter<'_, Ticket> {
        self.tickets.iter()
    }