Add missing space to error message

Author: Luis Vasconcellos

activerecord/lib/active_record/encryption/scheme.rb

@@ -82,7 +82,7 @@ def validate_keys!
 
         def validate_credential(key, error_message = "is not configured")
           unless ActiveRecord::Encryption.config.public_send(key).present?
-            raise Errors::Configuration, "#{key} #{error_message}. Please configure it via credential"\
+            raise Errors::Configuration, "#{key} #{error_message}. Please configure it via credential "\
               "active_record_encryption.#{key} or by setting config.active_record.encryption.#{key}"
           end
         end