fixed typo.md

Author: Kaitlin Vignali

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 # Contributing to Learn.co Curriculum
 
-We're really exited that you're about to contribute to the [open curriculum](https://learn.co/content-license) on [Learn.co](https://learn.co). If this is your first time contributing, please continue reading to learn how to make the most meaningful and useful impact possible.
+We're really excited that you're about to contribute to the [open curriculum](https://learn.co/content-license) on [Learn.co](https://learn.co). If this is your first time contributing, please continue reading to learn how to make the most meaningful and useful impact possible.
 
 ## Raising an Issue to Encourage a Contribution