chore(errors2): minor description wording change

This commit makes a minor change in the wording of the description of the errors2 exercise to avoid potential confusion, changing:

"A player of the game will type in how many items they want to buy, and the `total_cost` function will calculate the total cost of the tokens."
to
"A player of the game will type in how many items they want to buy, and the `total_cost` function will calculate the total cost of the items."

exercises/error_handling/errors2.rs

@@ -3,7 +3,7 @@
 // Say we're writing a game where you can buy items with tokens. All items cost
 // 5 tokens, and whenever you purchase items there is a processing fee of 1
 // token. A player of the game will type in how many items they want to buy, and
-// the `total_cost` function will calculate the total cost of the tokens. Since
+// the `total_cost` function will calculate the total cost of the items. Since
 // the player typed in the quantity, though, we get it as a string-- and they
 // might have typed anything, not just numbers!
 //