fix womFileType coercion (#47)

Co-authored-by: quekx <[email protected]>

backend/src/main/scala/cromwell/backend/standard/StandardAsyncExecutionActor.scala

@@ -171,7 +171,7 @@ trait StandardAsyncExecutionActor
           // decode url encoded values generated by the mapper
           val decoded_womValue = URLDecoder.decode(mapped_wom.valueString,"UTF-8")
           // convert to womfile again
-          WomFile(WomSingleFileType, decoded_womValue)
+          WomFile(womFile.womFileType, decoded_womValue)
         }
     )
   }