Implementing poc spec behavior in append route.

spec/test/features/control/append/error_unprocessable.feature

@@ -15,8 +15,8 @@ Feature: Kapow! server reject responses with semantic errors.
     Then I get 422 as response code
       And I get "Missing Mandatory Field" as response reason phrase
       And I get the following entity as response body:
-        | missing_mandatory_fields |
-        | "url_pattern", "method" |
+        | missing_mandatory_fields  |
+        | ["url_pattern", "method"] |
 
   Scenario: Error because of wrong route specification.
     If a request contains an invalid expression in the