Fix the pgrx links in the aggregate article. (#1516)

The links were explicitly referencing the then new version 0.3.0 but
this version isn't available anymore on docs.rs, so use the "latest"
version instead.

articles/postgresql-aggregates-with-rust.md

@@ -916,20 +916,20 @@ If you're looking for more materials about aggregates, the TimescaleDB folks wro
 
 [pgrx]: https://github.com/pgcentralfoundation/pgrx/
 [pgrx-issues]: https://github.com/pgcentralfoundation/pgrx/issues
-[pgrx-aggregate-aggregate]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html
-[pgrx-aggregate-aggregate-finalize]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#tymethod.finalize
-[pgrx-aggregate-aggregate-state]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#associatedtype.State
-[pgrx-aggregate-aggregate-combine]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#tymethod.combine
-[pgrx-aggregate-aggregate-parallel]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#associatedconstant.PARALLEL
-[pgrx::aggregate::Aggregate::ORDERED_SET]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#associatedconstant.ORDERED_SET
-[pgrx::aggregate::Aggregate::OrderedSetArgs]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#associatedtype.OrderedSetArgs
-[pgrx::aggregate::Aggregate::moving_state]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#tymethod.moving_state
-[pgrx::aggregate::Aggregate::moving_state_inverse]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#tymethod.moving_state_inverse
-[pgrx::aggregate::Aggregate::MovingState]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#associatedtype.MovingState
-[pgrx::aggregate::Aggregate::moving_state_finalize]: https://docs.rs/pgrx/0.3.0/pgrx/aggregate/trait.Aggregate.html#tymethod.moving_finalize
-[pgrx::datum::Internal]: https://docs.rs/pgrx/0.3.0/pgrx/datum/struct.Internal.html
-[pgrx-pg_aggregate]: https://docs.rs/pgrx/0.3.0/pgrx/attr.pg_aggregate.html
-[pgrx-postgrestype]: https://docs.rs/pgrx/0.3.0/pgrx/derive.PostgresType.html
+[pgrx-aggregate-aggregate]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html
+[pgrx-aggregate-aggregate-finalize]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#tymethod.finalize
+[pgrx-aggregate-aggregate-state]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#associatedtype.State
+[pgrx-aggregate-aggregate-combine]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#tymethod.combine
+[pgrx-aggregate-aggregate-parallel]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#associatedconstant.PARALLEL
+[pgrx::aggregate::Aggregate::ORDERED_SET]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#associatedconstant.ORDERED_SET
+[pgrx::aggregate::Aggregate::OrderedSetArgs]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#associatedtype.OrderedSetArgs
+[pgrx::aggregate::Aggregate::moving_state]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#tymethod.moving_state
+[pgrx::aggregate::Aggregate::moving_state_inverse]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#tymethod.moving_state_inverse
+[pgrx::aggregate::Aggregate::MovingState]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#associatedtype.MovingState
+[pgrx::aggregate::Aggregate::moving_state_finalize]: https://docs.rs/pgrx/latest/pgrx/aggregate/trait.Aggregate.html#tymethod.moving_finalize
+[pgrx::datum::Internal]: https://docs.rs/pgrx/latest/pgrx/datum/struct.Internal.html
+[pgrx-pg_aggregate]: https://docs.rs/pgrx/latest/pgrx/attr.pg_aggregate.html
+[pgrx-postgrestype]: https://docs.rs/pgrx/latest/pgrx/derive.PostgresType.html
 [pgrx-system-requirements]: https://github.com/pgcentralfoundation/pgrx/#system-requirements
 [plrust]: https://github.com/tcdi/plrust
 [rustup-rs]: https://rustup.rs/