remove ActiveModel::Errors#get deprecation for Rails 5.1

Author: Andrew Dang

lib/judge/validation.rb

@@ -33,7 +33,7 @@ def validate!
     end
 
     def as_json(options = {})
-      record.errors.get(@attribute) || []
+      record.errors[@attribute] || []
     end
   end
 
@@ -51,4 +51,4 @@ def method_missing(*args)
     end
   end
 
-end
+end