Fix typo in Expense Tracker link in README.md

Author: Raffaele Marcello

README.md

@@ -108,7 +108,7 @@ Run:
 - [Develop a chat based on websockets](./challenges/chatwebsockets/chatwebsockets.md)
 - [Behavior Driven Development (BDD) challenge](./challenges/bdd/README.md)
 - [Analysis cryptocurrency market](./challenges/cryptoanalisis/crypto.md)
-- [Expnse Tracker](./challenges/expensetracker/README.md)
+- [Expense Tracker](./challenges/expensetracker/README.md)
 
 ## Quick Links