Update currency API URL

[i-midhunbabu]

Updated the API endpoint format.

Check: https://github.com/fawazahmed0/exchange-api/blob/main/MIGRATION.md

---

What's Changed

1. Base URL Updated

const BASE_URL = "https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@latest/v1/currencies";

2. Endpoint Structure Refactored

const URL = `${BASE_URL}/${fromCurr.value.toLowerCase()}.json`;

let rate = data[fromCurr.value.toLowerCase()][toCurr.value.toLowerCase()];