Typo

Fixing typo.

Author: Eduard Sergeev

Library/Core/Validatable.swift

@@ -21,7 +21,7 @@ public struct ValidationError: Error, CustomStringConvertible {
 
 public protocol Validatable {
   /**
-   Validates this entity and throws if it encounters a invalid situation, a validatable should also validate it sub-validatables if it has any.
+   Validates this entity and throws if it encounters an invalid situation, a validatable should also validate it sub-validatables if it has any.
 
    - throws: If there the configuration error a ValidationError is thrown
    */