Update instructions for Erlang-Extraction Exercise

[RickHPotter]

https://exercism.org/tracks/gleam/exercises/erlang-extraction

In the exercise, it says

The function should take three arguments:

The GbTree to insert into.
The key to insert.
The value to insert.

But the correct order is as follows

insert(Key, Value, Tree1) Inserts Key with value Value into Tree1 and returns the new tree. Assumes that the key is not present in the tree, crashes otherwise.

[RickHPotter]

I just realised that the delete_any external function is also with the wrong order. It should be key, Tree1, but the exercise says otherwise.