Update README.md

Author: alesanchezr

README.md

@@ -53,7 +53,7 @@ Each exercise is a small React application containing the following files:
 
 > Note: The exercises have automatic grading, but it's very rigid and strict, my recommendation is to not take the tests too serious and use them only as a suggestion, or you may get frustrated.
 
-## Contributors.
+## Contributors
 
 Thanks goes to these wonderful people ([emoji key](https://github.com/kentcdodds/all-contributors#emoji-key)):