Fix typo in entry for Tax Data API

Fix spelling of Cors field. `Unkown` is incorrect. Fix spells it `Unknown` as it is spelled for all other entries.

Fixes #3262

README.md

@@ -776,7 +776,7 @@ API | Description | Auth | HTTPS | CORS |
 | [SmartAPI](https://smartapi.angelbroking.com/) | Gain access to set of <SmartAPI> and create end-to-end broking services | `apiKey` | Yes | Unknown |
 | [StockData](https://www.StockData.org) | Real-Time, Intraday & Historical Market Data, News and Sentiment API | `apiKey` | Yes | Yes |
 | [Styvio](https://www.Styvio.com) | Realtime and historical stock data and current stock sentiment | `apiKey` | Yes | Unknown |
-| [Tax Data API](https://apilayer.com/marketplace/tax_data-api) | Instant VAT number and tax validation across the globe | `apiKey` | Yes | Unkown |
+| [Tax Data API](https://apilayer.com/marketplace/tax_data-api) | Instant VAT number and tax validation across the globe | `apiKey` | Yes | Unknown |
 | [Tradier](https://developer.tradier.com) | US equity/option market data (delayed, intraday, historical) | `OAuth` | Yes | Yes |
 | [Twelve Data](https://twelvedata.com/) | Stock market data (real-time & historical) | `apiKey` | Yes | Unknown |
 | [WallstreetBets](https://dashboard.nbshare.io/apps/reddit/api/) | WallstreetBets Stock Comments Sentiment Analysis | No | Yes | Unknown |