Fixed a typo

Author: javiereguiluz

components/validator/introduction.rst

@@ -24,7 +24,7 @@ Usage
 The Validator component behavior is based on two concepts:
 
 * Contraints, which define the rules to be validated;
-* Validators, which are the classees that contain the actual validation logic.
+* Validators, which are the classes that contain the actual validation logic.
 
 The following example shows how to validate that a string is at least 10
 characters long::