Change method used to retrieve rack status

Fixes #1456

Author: Adrian Hooper

lib/jsonapi/error.rb

@@ -17,7 +17,7 @@ def initialize(options = {})
       @source         = options[:source]
       @links          = options[:links]
 
-      @status         = Rack::Utils::SYMBOL_TO_STATUS_CODE[options[:status]].to_s
+      @status         = Rack::Utils.status_code(options[:status]).to_s
       @meta           = options[:meta]
     end
 
@@ -48,7 +48,7 @@ def update_with_overrides(error_object_overrides)
 
       if error_object_overrides[:status]
         # :nocov:
-        @status         = Rack::Utils::SYMBOL_TO_STATUS_CODE[error_object_overrides[:status]].to_s
+        @status         = Rack::Utils.status_code(error_object_overrides[:status]).to_s
         # :nocov:
       end
       @meta           = error_object_overrides[:meta] || @meta