Update fundamentals.py

Error in supplying timescale values resulted in misleading ValueError - 

```
ValueError: Illegal argument: timescale must be one of: ['income', 'balance-sheet', 'cash-flow']
```

yfinance/scrapers/fundamentals.py

@@ -79,7 +79,7 @@ def _fetch_time_series(self, name, timescale, proxy=None):
         if name not in allowed_names:
             raise ValueError(f"Illegal argument: name must be one of: {allowed_names}")
         if timescale not in allowed_timescales:
-            raise ValueError(f"Illegal argument: timescale must be one of: {allowed_names}")
+            raise ValueError(f"Illegal argument: timescale must be one of: {allowed_timescales}")
 
         try:
             statement = self._create_financials_table(name, timescale, proxy)