[B] Fix missing closing brackets in ItemStack.addEnchantment error message. Fixes Bukkit-4126

**The issue:**

The error message is missing a closing braket.

**Justification for this PR:**

The error message looks like being incomplete, although it is complete.
There should not be any bracket issues in the messages.

**PR Breakdown:**

Adds the missing closing bracket to the error message's text.
current: "Enchantment level is either too low or too high (given 100, bounds are 1 to 5"
fixed: "Enchantment level is either too low or too high (given 100, bounds are 1 to 5)"
Although this is just a minor mistake, but error message should be correctly too.

**Testing Results and Materials:**

None

**JIRA-Ticket:**

https://bukkit.atlassian.net/browse/BUKKIT-4126