update doc v9 url to v10

Author: Dean Karn

doc.go

@@ -5,7 +5,7 @@ based on tags.
 It can also handle Cross-Field and Cross-Struct validation for nested structs
 and has the ability to dive into arrays and maps of any type.
 
-see more examples https://github.com/go-playground/validator/tree/v9/_examples
+see more examples https://github.com/go-playground/validator/tree/master/_examples
 
 Validation Functions Return Type error