Fix currency API endpoint accepting only lowercase currency strings

Signed-off-by: Lukáš Kucharczyk <lukas@kucharczyk.xyz>

games/tasks.py

@@ -33,8 +33,9 @@ def convert_prices():
 
         if not exchange_rate:
             try:
+                # this API endpoint only accepts lowercase currency string
                 response = requests.get(
-                    f"https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@{year}-01-01/v1/currencies/{currency_from}.json"
+                    f"https://cdn.jsdelivr.net/npm/@fawazahmed0/currency-api@{year}-01-01/v1/currencies/{currency_from.lower()}.json"
                 )
                 response.raise_for_status()
                 data = response.json()