docs(tiered pricing): 📝 Update price for 50 subscriptions to 199 € per subscription

Author: JavierCane

exercises/tiered_pricing/README.md

@@ -37,7 +37,7 @@ development process:
 | 26            |      199 € | 5174 € |
 | 27            |      199 € | 5373 € |
 | 28            |      199 € | 5572 € |
-| 50            |      149 € | 9950 € |
+| 50            |      199 € | 9950 € |
 | 51            |      149 € | 7599 € |
 | 52            |      149 € | 7748 € |