docs: Fix type in VALIDATION.md

Author: nikital

docs/VALIDATION.md

@@ -35,7 +35,7 @@ const failure = 'some error'.fail()
 ### map
 
 ```scala
-Validation[E,A].map(fn: A => B): Validation[E,A]
+Validation[E,A].map(fn: A => B): Validation[E,B]
 ```
 
 `map` takes a function (A => B) and applies that function to the value inside the `success` side of the `Validation` and returns another `Validation`. For example: