title: RestKit: Data not mappable unless `pattern` is `nil`
body: <p>I load data from the following URL:</p>
  
  <pre><code>https://myserver.com/api/kitchens/0af569e6-3e7d-4d6d-b8ca-7a70f93160c9/recipes/18488b51-04e0-4146-8ac6-05106db14024
  </code></pre>
  
  <p>The data looks like so:</p>
  
  <pre><code>{
    "recipe": {
      "id": "18488b51-04e0-4146-8ac6-05106db14024",
      "kitchen-id": "0af569e6-3e7d-4d6d-b8ca-7a70f93160c9",
      "rating": "",
      "title": "My recipe",
      "author": “John”,
      "date": "2014-05-10",
      "location": “Paris,
      "servings": 4,
      "customer-rating": 5.0,
      "ingredients": [
  
      ]
    }
  }
  </code></pre>
  
  <p>I can map the data so my mapping is fine. However, as soon as I specify a pattern, I no longer get any data mapped. What is wrong with my pattern?</p>
  
  <p>Here a comparison:</p>
  
  <pre><code>PATTERN
  /api/kitchens/:kitchenID/recipes/:recipeID
  URL PATH
  /api/kitchens/0af569e6-3e7d-4d6d-b8ca-7a70f93160c9/recipes/18488b51-04e0-4146-8ac6-05106db14024
  </code></pre>
  
  <p>My Mapping code</p>
  
  <pre><code>    RKEntityMapping *mapping = [RKEntityMapping mappingForEntityForName:@"Recipe" inManagedObjectStore:self.service.managedObjectStore];
  NSDictionary *map = @{
                        @"id": @"id",
                        @"title": @"title",
                        @"rating": @"rating",
                        @"date": @"createdOn",
                        @"author": @"author",
                        @"servings": @"servings",
                        @"customer-rating": @"customerRating",
                        };
  [mapping addAttributeMappingsFromDictionary:map];
  result.identificationAttributes = @[@"id"];
  
  
  // This does not work
      NSString *pattern = @"/api/kitchens/:kitchenID/recipes/:recipeID"
  
  // This works
  NSString *pattern = nil;
  
      RKResponseDescriptor *responseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:mapping method:RKRequestMethodAny pathPattern:pattern keyPath: @“recipe” statusCodes:statusCodes];
  </code></pre>